Kills /obj/shapeshift_holder, replaces it with /datum/status_effect/shapechange_mob, also does a lot of Wabbajack refactoring (#69091)

About The Pull Request

    Deletes /obj/shapeshift_holder, replaces it with /datum/status_effect/shapechange_mob
    Refactors Heretic worm form into a shapeshift spell
    Refactors Wabbajack, and associated code

Fixes #69117
Fixes #65653
Fixes #59127
Fixes #52786
Why It's Good For The Game

/obj/shapeshift_holder was one of the worst remaining abuses of /obj direct subtypes, so I replaced it with a cool fancy datum.

This also decouples the shapeshifting behavior entirely from the shapeshifting spell. So we have support for shapeshifted mobs not sourced from a spell. Which is neat, we could technically swap Wabbajack to use this in the future.
Changelog

cl Melbert
fix: Wabbajacking a shapeshifted mob no longer runtimes horribly. When a shapeshifted mob is wabbajacked, they'll now be removed from their shapeshift and stunned.
fix: Transforming via a shapeshift should no longer rob you of your hearing / runechat awareness.
fix: Shapeshifting plays nicer with holoparasites.
fix: Being polymorphed from a xeno to a non-xeno correctly makes you a non-xeno
refactor: Refactored shapeshifting, the shapeshift holder is now a status effect instead of an object.
refactor: Heretic worm form is a shapeshift spell now, this might have some minor behavioral changes but should overall be the same.
refactor: Refactored Wabbajack (+ cursed pool). Overall a bit more clean / consistent behavior.
/cl

code/__DEFINES/dcs/signals/signals_mob/signals_mob_living.dm

@@ -94,8 +94,18 @@
 
 ///From obj/item/toy/crayon/spraycan
 #define COMSIG_LIVING_MOB_PAINTED "living_mob_painted"
-///From mob/living/proc/wabbajack_act
-#define COMSIG_LIVING_WABBAJACKED "living_wabbajacked"
+
+///From mob/living/proc/wabbajack(): (randomize_type)
+#define COMSIG_LIVING_PRE_WABBAJACKED "living_mob_wabbajacked"
+	/// Return to stop the rest of the wabbajack from triggering.
+	#define STOP_WABBAJACK (1<<0)
+///From mob/living/proc/on_wabbajack(): (mob/living/new_mob)
+#define COMSIG_LIVING_ON_WABBAJACKED "living_wabbajacked"
+
+/// From /datum/status_effect/shapechange_mob/on_apply(): (mob/living/shape)
+#define COMSIG_LIVING_SHAPESHIFTED "living_shapeshifted"
+/// From /datum/status_effect/shapechange_mob/after_unchange(): (mob/living/caster)
+#define COMSIG_LIVING_UNSHAPESHIFTED "living_unshapeshifted"
 
 ///From /obj/effect/rune/convert/do_sacrifice() : (list/invokers)
 #define COMSIG_LIVING_CULT_SACRIFICED "living_cult_sacrificed"

code/__DEFINES/mobs.dm

@@ -484,6 +484,16 @@
 //Wabbacjack staff projectiles
 #define WABBAJACK (1<<6)
 
+// Randomization keys for calling wabbajack with.
+// Note the contents of these keys are important, as they're displayed to the player
+// Ex: (You turn into a "monkey", You turn into a "xenomorph")
+#define WABBAJACK_MONKEY "monkey"
+#define WABBAJACK_ROBOT "robot"
+#define WABBAJACK_SLIME "slime"
+#define WABBAJACK_XENO "xenomorph"
+#define WABBAJACK_HUMAN "humanoid"
+#define WABBAJACK_ANIMAL "animal"
+
 // Reasons a defibrilation might fail
 #define DEFIB_POSSIBLE (1<<0)
 #define DEFIB_FAIL_SUICIDE (1<<1)

code/__DEFINES/status_effects.dm

@@ -37,5 +37,4 @@
 
 #define STASIS_CHEMICAL_EFFECT "stasis_chemical"
 
-#define STASIS_ASCENSION_EFFECT "heretic_ascension"
-
+#define STASIS_SHAPECHANGE_EFFECT "stasis_shapechange"

code/datums/elements/content_barfer.dm

@@ -13,10 +13,10 @@
 	if(!isliving(target))
 		return ELEMENT_INCOMPATIBLE
 
-	RegisterSignal(target, list(COMSIG_LIVING_DEATH, COMSIG_LIVING_WABBAJACKED), .proc/barf_contents)
+	RegisterSignal(target, list(COMSIG_LIVING_DEATH, COMSIG_LIVING_ON_WABBAJACKED), .proc/barf_contents)
 
 /datum/element/content_barfer/Detach(datum/target)
-	UnregisterSignal(target, list(COMSIG_LIVING_DEATH, COMSIG_LIVING_WABBAJACKED))
+	UnregisterSignal(target, list(COMSIG_LIVING_DEATH, COMSIG_LIVING_ON_WABBAJACKED))
 	return ..()
 
 /datum/element/content_barfer/proc/barf_contents(mob/living/target)

code/modules/antagonists/heretic/knowledge/flesh_lore.dm

@@ -303,7 +303,7 @@
 	. = ..()
 	priority_announce("[generate_heretic_text()] Ever coiling vortex. Reality unfolded. ARMS OUTREACHED, THE LORD OF THE NIGHT, [user.real_name] has ascended! Fear the ever twisting hand! [generate_heretic_text()]", "[generate_heretic_text()]", ANNOUNCER_SPANOMALIES)
 
-	var/datum/action/cooldown/spell/shed_human_form/worm_spell = new(user.mind)
+	var/datum/action/cooldown/spell/shapeshift/shed_human_form/worm_spell = new(user.mind)
 	worm_spell.Grant(user)
 
 	user.client?.give_award(/datum/award/achievement/misc/flesh_ascension, user)

code/modules/antagonists/heretic/magic/flesh_ascension.dm

@@ -1,4 +1,4 @@
-/datum/action/cooldown/spell/shed_human_form
+/datum/action/cooldown/spell/shapeshift/shed_human_form
 	name = "Shed form"
 	desc = "Shed your fragile form, become one with the arms, become one with the emperor. \
 		Causes heavy amounts of brain damage and sanity loss to nearby mortals."
@@ -7,49 +7,41 @@
 	button_icon_state = "worm_ascend"
 
 	school = SCHOOL_FORBIDDEN
-	cooldown_time = 10 SECONDS
 
 	invocation = "REALITY UNCOIL!"
 	invocation_type = INVOCATION_SHOUT
 	spell_requirements = NONE
 
+	possible_shapes = list(/mob/living/simple_animal/hostile/heretic_summon/armsy/prime)
+
 	/// The length of our new wormy when we shed.
 	var/segment_length = 10
 	/// The radius around us that we cause brain damage / sanity damage to.
 	var/scare_radius = 9
 
-/datum/action/cooldown/spell/shed_human_form/is_valid_target(atom/cast_on)
-	return isliving(cast_on)
+/datum/action/cooldown/spell/shapeshift/shed_human_form/do_shapeshift(mob/living/caster)
+	// When we transform into the worm, everyone nearby gets freaked out
+	for(var/mob/living/carbon/human/nearby_human in view(scare_radius, caster))
+		if(IS_HERETIC_OR_MONSTER(nearby_human))
+			continue
 
-/datum/action/cooldown/spell/shed_human_form/cast(mob/living/cast_on)
-	. = ..()
-	if(istype(cast_on, /mob/living/simple_animal/hostile/heretic_summon/armsy/prime))
-		var/mob/living/simple_animal/hostile/heretic_summon/armsy/prime/old_armsy = cast_on
-		var/mob/living/our_heretic = locate() in old_armsy
+		// 25% chance to cause a trauma
+		if(prob(25))
+			var/datum/brain_trauma/trauma = pick(subtypesof(BRAIN_TRAUMA_MILD) + subtypesof(BRAIN_TRAUMA_SEVERE))
+			nearby_human.gain_trauma(trauma, TRAUMA_RESILIENCE_LOBOTOMY)
+		// And a negative moodlet
+		nearby_human.add_mood_event("gates_of_mansus", /datum/mood_event/gates_of_mansus)
 
-		if(our_heretic.remove_status_effect(/datum/status_effect/grouped/stasis, STASIS_ASCENSION_EFFECT))
-			our_heretic.forceMove(old_armsy.loc)
+	return ..()
 
-		old_armsy.mind.transfer_to(our_heretic, TRUE)
-		segment_length = old_armsy.get_length()
-		qdel(old_armsy)
+/datum/action/cooldown/spell/shapeshift/shed_human_form/do_unshapeshift(mob/living/simple_animal/hostile/heretic_summon/armsy/caster)
+	if(istype(caster))
+		segment_length = caster.get_length()
 
-	else
-		var/mob/living/simple_animal/hostile/heretic_summon/armsy/prime/new_armsy = new(cast_on.loc, TRUE, segment_length)
+	return ..()
 
-		cast_on.mind.transfer_to(new_armsy, TRUE)
-		cast_on.forceMove(new_armsy)
-		cast_on.apply_status_effect(/datum/status_effect/grouped/stasis, STASIS_ASCENSION_EFFECT)
-
-		// They see the very reality uncoil before their eyes.
-		for(var/mob/living/carbon/human/nearby_human in view(scare_radius, new_armsy))
-			if(IS_HERETIC_OR_MONSTER(nearby_human))
-				continue
-			nearby_human.add_mood_event("gates_of_mansus", /datum/mood_event/gates_of_mansus)
-
-			if(prob(25))
-				var/datum/brain_trauma/trauma = pick(subtypesof(BRAIN_TRAUMA_MILD) + subtypesof(BRAIN_TRAUMA_SEVERE))
-				nearby_human.gain_trauma(trauma, TRAUMA_RESILIENCE_LOBOTOMY)
+/datum/action/cooldown/spell/shapeshift/shed_human_form/create_shapeshift_mob(atom/loc)
+	return new shapeshift_type(loc, TRUE, segment_length)
 
 /datum/action/cooldown/spell/worm_contract
 	name = "Force Contract"

code/modules/antagonists/xeno/xeno.dm

@@ -42,3 +42,13 @@
 		mind.add_antag_datum(/datum/antagonist/xeno)
 		mind.set_assigned_role(SSjob.GetJobType(/datum/job/xenomorph))
 		mind.special_role = ROLE_ALIEN
+
+/mob/living/carbon/alien/on_wabbajacked(mob/living/new_mob)
+	. = ..()
+	if(!mind)
+		return
+	if(isalien(new_mob))
+		return
+	mind.remove_antag_datum(/datum/antagonist/xeno)
+	mind.set_assigned_role(SSjob.GetJobType(/datum/job/unassigned))
+	mind.special_role = null

code/modules/events/wizard/magicarp.dm

@@ -40,13 +40,23 @@
 	gold_core_spawnable = NO_SPAWN
 	random_color = FALSE
 
-	var/allowed_projectile_types = list(/obj/projectile/magic/change, /obj/projectile/magic/animate, /obj/projectile/magic/resurrection,
-	/obj/projectile/magic/death, /obj/projectile/magic/teleport, /obj/projectile/magic/door, /obj/projectile/magic/fireball,
-	/obj/projectile/magic/spellblade, /obj/projectile/magic/arcane_barrage)
+	/// List of all projectiles we can fire.
+	/// Non-static, because subtypes can have their own lists.
+	var/list/allowed_projectile_types = list(
+		/obj/projectile/magic/animate,
+		/obj/projectile/magic/arcane_barrage,
+		/obj/projectile/magic/change,
+		/obj/projectile/magic/death,
+		/obj/projectile/magic/door,
+		/obj/projectile/magic/fireball,
+		/obj/projectile/magic/resurrection,
+		/obj/projectile/magic/spellblade,
+		/obj/projectile/magic/teleport,
+	)
 
 /mob/living/simple_animal/hostile/carp/ranged/Initialize(mapload)
 	projectiletype = pick(allowed_projectile_types)
-	. = ..()
+	return ..()
 
 /mob/living/simple_animal/hostile/carp/ranged/chaos
 	name = "chaos magicarp"
@@ -58,14 +68,27 @@
 
 /mob/living/simple_animal/hostile/carp/ranged/chaos/Shoot()
 	projectiletype = pick(allowed_projectile_types)
-	..()
+	return ..()
 
 /mob/living/simple_animal/hostile/carp/ranged/xenobiology // these are for the xenobio gold slime pool
 	gold_core_spawnable = HOSTILE_SPAWN
-	allowed_projectile_types = list(/obj/projectile/magic/animate, /obj/projectile/magic/teleport,
-	/obj/projectile/magic/door, /obj/projectile/magic/fireball, /obj/projectile/magic/spellblade, /obj/projectile/magic/arcane_barrage) //thanks Lett1
+
+	allowed_projectile_types = list(
+		/obj/projectile/magic/animate,
+		/obj/projectile/magic/teleport,
+		/obj/projectile/magic/door,
+		/obj/projectile/magic/fireball,
+		/obj/projectile/magic/spellblade,
+		/obj/projectile/magic/arcane_barrage,
+	) //thanks Lett1
 
 /mob/living/simple_animal/hostile/carp/ranged/chaos/xenobiology
 	gold_core_spawnable = HOSTILE_SPAWN
-	allowed_projectile_types = list(/obj/projectile/magic/animate, /obj/projectile/magic/teleport,
-	/obj/projectile/magic/door, /obj/projectile/magic/fireball, /obj/projectile/magic/spellblade, /obj/projectile/magic/arcane_barrage)
+	allowed_projectile_types = list(
+		/obj/projectile/magic/animate,
+		/obj/projectile/magic/teleport,
+		/obj/projectile/magic/door,
+		/obj/projectile/magic/fireball,
+		/obj/projectile/magic/spellblade,
+		/obj/projectile/magic/arcane_barrage,
+	)

code/modules/mapfluff/ruins/icemoonruin_code/hotsprings.dm

@@ -19,28 +19,23 @@
 	. = ..()
 	if(!isliving(arrived))
 		return
-	var/mob/living/L = arrived
-	if(!L.client || L.incorporeal_move || !L.mind)
+	var/mob/living/to_transform = arrived
+	var/datum/mind/transforming_mind = to_transform.mind
+	if(!to_transform.client || to_transform.incorporeal_move || !transforming_mind)
 		return
-	if(HAS_TRAIT(L.mind, TRAIT_HOT_SPRING_CURSED)) // no double dipping
+	if(HAS_TRAIT(transforming_mind, TRAIT_HOT_SPRING_CURSED)) // no double dipping
 		return
 
-	ADD_TRAIT(L.mind, TRAIT_HOT_SPRING_CURSED, TRAIT_GENERIC)
-	var/random_choice = pick("Mob", "Appearance")
-	switch(random_choice)
-		if("Mob")
-			L = L.wabbajack("animal")
-		if("Appearance")
-			var/mob/living/carbon/human/H = L.wabbajack("humanoid")
-			randomize_human(H)
-			var/list/all_species = list()
-			for(var/stype in subtypesof(/datum/species))
-				var/datum/species/S = stype
-				if(initial(S.changesource_flags) & RACE_SWAP)
-					all_species += stype
-			var/random_race = pick(all_species)
-			H.set_species(random_race)
-			L = H
-	var/turf/T = find_safe_turf(extended_safety_checks = TRUE, dense_atoms = FALSE)
-	L.forceMove(T)
-	to_chat(L, span_notice("You blink and find yourself in [get_area_name(T)]."))
+	ADD_TRAIT(transforming_mind, TRAIT_HOT_SPRING_CURSED, TRAIT_GENERIC)
+	var/mob/living/transformed_mob = to_transform.wabbajack(pick(WABBAJACK_HUMAN, WABBAJACK_ANIMAL), change_flags = RACE_SWAP)
+	if(!transformed_mob)
+		// Wabbajack failed, maybe the mob had godmode or something.
+		if(!QDELETED(to_transform))
+			to_chat(to_transform, span_notice("The water seems to have no effect on you."))
+		// because it failed, let's allow them to try again in a lil' bit
+		addtimer(TRAIT_CALLBACK_REMOVE(transforming_mind, TRAIT_HOT_SPRING_CURSED, TRAIT_GENERIC), 10 SECONDS)
+		return
+
+	var/turf/return_turf = find_safe_turf(extended_safety_checks = TRUE, dense_atoms = FALSE)
+	transformed_mob.forceMove(return_turf)
+	to_chat(transformed_mob, span_notice("You blink and find yourself in [get_area_name(return_turf)]."))

code/modules/mining/lavaland/tendril_loot.dm

@@ -168,7 +168,7 @@
 /obj/item/clothing/neck/necklace/memento_mori/proc/check_health(mob/living/source)
 	SIGNAL_HANDLER
 
-	var/list/guardians = source.hasparasites()
+	var/list/guardians = source.get_all_linked_holoparasites()
 	if(!length(guardians))
 		return
 	if(source.health <= HEALTH_THRESHOLD_DEAD)

code/modules/mob/living/carbon/human/species_types/vampire.dm

@@ -56,9 +56,6 @@
 	vampire.blood_volume -= 0.125 * delta_time
 	if(vampire.blood_volume <= BLOOD_VOLUME_SURVIVE)
 		to_chat(vampire, span_danger("You ran out of blood!"))
-		var/obj/shapeshift_holder/holder = locate() in vampire
-		if(holder)
-			holder.shape.dust() //vampires do not have batform anymore, but this would still lead to very weird stuff with other shapeshift holders
 		vampire.dust()
 	var/area/A = get_area(vampire)
 	if(istype(A, /area/station/service/chapel))

code/modules/mob/living/living.dm

@@ -1193,18 +1193,22 @@
 	. = ..()
 
 // Used in polymorph code to shapeshift mobs into other creatures
-/mob/living/proc/wabbajack(randomize)
-	// If the mob has a shapeshifted form, we want to pull out the reference of the caster's original body from it.
-	// We then want to restore this original body through the shapeshift holder itself.
-	var/obj/shapeshift_holder/shapeshift = locate() in src
-	if(shapeshift)
-		shapeshift.restore()
-		if(shapeshift.stored != src) // To reduce the risk of an infinite loop.
-			return shapeshift.stored.wabbajack(randomize)
-
+/**
+ * Polymorphs our mob into another mob.
+ * If successful, our current mob is qdeleted!
+ *
+ * what_to_randomize - what are we randomizing the mob into? See the defines for valid options.
+ * change_flags - only used for humanoid randomization (currently), what pool of changeflags should we draw from?
+ *
+ * Returns a mob (what our mob turned into) or null (if we failed).
+ */
+/mob/living/proc/wabbajack(what_to_randomize, change_flags = WABBAJACK)
 	if(stat == DEAD || notransform || (GODMODE & status_flags))
 		return
 
+	if(SEND_SIGNAL(src, COMSIG_LIVING_PRE_WABBAJACKED, what_to_randomize) & STOP_WABBAJACK)
+		return
+
 	notransform = TRUE
 	ADD_TRAIT(src, TRAIT_IMMOBILIZED, MAGIC_TRAIT)
 	ADD_TRAIT(src, TRAIT_HANDS_BLOCKED, MAGIC_TRAIT)
@@ -1231,51 +1235,64 @@
 
 	var/mob/living/new_mob
 
-	if(!randomize)
-		randomize = pick("monkey","robot","slime","xeno","humanoid","animal")
-	switch(randomize)
-		if("monkey")
+	var/static/list/possible_results = list(
+		WABBAJACK_MONKEY,
+		WABBAJACK_ROBOT,
+		WABBAJACK_SLIME,
+		WABBAJACK_XENO,
+		WABBAJACK_HUMAN,
+		WABBAJACK_ANIMAL,
+	)
+
+	// If we weren't passed one, pick a default one
+	what_to_randomize ||= pick(possible_results)
+
+	switch(what_to_randomize)
+		if(WABBAJACK_MONKEY)
 			new_mob = new /mob/living/carbon/human/species/monkey(loc)
 
-		if("robot")
-			var/robot = pick(
-				200 ; /mob/living/silicon/robot,
-				/mob/living/silicon/robot/model/syndicate,
-				/mob/living/silicon/robot/model/syndicate/medical,
-				/mob/living/silicon/robot/model/syndicate/saboteur,
-				200 ; /mob/living/simple_animal/drone/polymorphed,
+		if(WABBAJACK_ROBOT)
+			var/static/list/robot_options = list(
+				/mob/living/silicon/robot = 200,
+				/mob/living/simple_animal/drone/polymorphed = 200,
+				/mob/living/silicon/robot/model/syndicate = 1,
+				/mob/living/silicon/robot/model/syndicate/medical = 1,
+				/mob/living/silicon/robot/model/syndicate/saboteur = 1,
 			)
-			new_mob = new robot(loc)
+
+			var/picked_robot = pick(robot_options)
+			new_mob = new picked_robot(loc)
 			if(issilicon(new_mob))
+				var/mob/living/silicon/robot/created_robot = new_mob
 				new_mob.gender = gender
 				new_mob.invisibility = 0
 				new_mob.job = JOB_CYBORG
-				var/mob/living/silicon/robot/Robot = new_mob
-				Robot.lawupdate = FALSE
-				Robot.connected_ai = null
-				Robot.mmi.transfer_identity(src) //Does not transfer key/client.
-				Robot.clear_inherent_laws(announce = FALSE)
-				Robot.clear_zeroth_law(announce = FALSE)
+				created_robot.lawupdate = FALSE
+				created_robot.connected_ai = null
+				created_robot.mmi.transfer_identity(src) //Does not transfer key/client.
+				created_robot.clear_inherent_laws(announce = FALSE)
+				created_robot.clear_zeroth_law(announce = FALSE)
 
-		if("slime")
+		if(WABBAJACK_SLIME)
 			new_mob = new /mob/living/simple_animal/slime/random(loc)
 
-		if("xeno")
-			var/xeno_type
+		if(WABBAJACK_XENO)
+			var/picked_xeno_type
+
 			if(ckey)
-				xeno_type = pick(
+				picked_xeno_type = pick(
 					/mob/living/carbon/alien/humanoid/hunter,
 					/mob/living/carbon/alien/humanoid/sentinel,
 				)
 			else
-				xeno_type = pick(
+				picked_xeno_type = pick(
 					/mob/living/carbon/alien/humanoid/hunter,
 					/mob/living/simple_animal/hostile/alien/sentinel,
 				)
-			new_mob = new xeno_type(loc)
+			new_mob = new picked_xeno_type(loc)
 
-		if("animal")
-			var/path = pick(
+		if(WABBAJACK_ANIMAL)
+			var/picked_animal = pick(
 				/mob/living/simple_animal/hostile/carp,
 				/mob/living/simple_animal/hostile/bear,
 				/mob/living/simple_animal/hostile/mushroom,
@@ -1311,17 +1328,17 @@
 				/mob/living/simple_animal/pet/dog/breaddog,
 				/mob/living/simple_animal/chick,
 			)
-			new_mob = new path(loc)
+			new_mob = new picked_animal(loc)
 
-		if("humanoid")
-			var/mob/living/carbon/human/new_human = new (loc)
+		if(WABBAJACK_HUMAN)
+			var/mob/living/carbon/human/new_human = new(loc)
 
+			// 50% chance that we'll also randomice race
 			if(prob(50))
 				var/list/chooseable_races = list()
-				for(var/speciestype in subtypesof(/datum/species))
-					var/datum/species/S = speciestype
-					if(initial(S.changesource_flags) & WABBAJACK)
-						chooseable_races += speciestype
+				for(var/datum/species/species_type as anything in subtypesof(/datum/species))
+					if(initial(species_type.changesource_flags) & change_flags)
+						chooseable_races += species_type
 
 				if(length(chooseable_races))
 					new_human.set_species(pick(chooseable_races))
@@ -1332,45 +1349,49 @@
 			new_human.dna.update_dna_identity()
 			new_mob = new_human
 
+		else
+			stack_trace("wabbajack() was called without an invalid randomization choice. ([what_to_randomize])")
+
 	if(!new_mob)
 		return
 
+	to_chat(src, span_hypnophrase(span_big("Your form morphs into that of a [what_to_randomize]!")))
+
+	// And of course, make sure they get policy for being transformed
+	var/poly_msg = get_policy(POLICY_POLYMORPH)
+	if(poly_msg)
+		to_chat(src, poly_msg)
+
 	// Some forms can still wear some items
 	for(var/obj/item/item as anything in item_contents)
 		new_mob.equip_to_appropriate_slot(item)
 
-	log_message("became [new_mob.name]([new_mob.type])", LOG_ATTACK, color="orange")
+	// I don't actually know why we do this
 	new_mob.set_combat_mode(TRUE)
-	wabbajack_act(new_mob)
-	to_chat(new_mob, span_warning("Your form morphs into that of a [randomize]."))
 
-	var/poly_msg = get_policy(POLICY_POLYMORPH)
-	if(poly_msg)
-		to_chat(new_mob, poly_msg)
+	// on_wabbajack is where we handle setting up the name,
+	// transfering the mind and observerse, and other miscellaneous
+	// actions that should be done before we delete the original mob.
+	on_wabbajacked(new_mob)
 
-	transfer_observers_to(new_mob)
-
-	. = new_mob
 	qdel(src)
+	return new_mob
 
 // Called when we are hit by a bolt of polymorph and changed
 // Generally the mob we are currently in is about to be deleted
-/mob/living/proc/wabbajack_act(mob/living/new_mob)
-	SEND_SIGNAL(src, COMSIG_LIVING_WABBAJACKED, new_mob)
-	log_message("was wabbajack polymorphed into: [new_mob.name]([new_mob.type]).", LOG_GAME)
+/mob/living/proc/on_wabbajacked(mob/living/new_mob)
+	log_message("became [new_mob.name] ([new_mob.type])", LOG_ATTACK, color = "orange")
+	SEND_SIGNAL(src, COMSIG_LIVING_ON_WABBAJACKED, new_mob)
 	new_mob.name = real_name
 	new_mob.real_name = real_name
 
+	// Transfer mind to the new mob (also handles actions and observers and stuff)
 	if(mind)
 		mind.transfer_to(new_mob)
-	else
-		new_mob.key = key
 
-	for(var/para in hasparasites())
-		var/mob/living/simple_animal/hostile/guardian/G = para
-		G.summoner = new_mob
-		G.Recall()
-		to_chat(G, span_holoparasite("Your summoner has changed form!"))
+	// Well, no mmind, guess we should try to move a key over
+	else if(key)
+		new_mob.key = key
 
 /mob/living/proc/unfry_mob() //Callback proc to tone down spam from multiple sizzling frying oil dipping.
 	REMOVE_TRAIT(src, TRAIT_OIL_FRIED, "cooking_oil_react")

code/modules/mob/living/simple_animal/guardian/guardian.dm

@@ -68,7 +68,43 @@ GLOBAL_LIST_EMPTY(parasites) //all currently existing/living guardians
 	GLOB.parasites += src
 	updatetheme(theme)
 	AddElement(/datum/element/simple_flying)
-	. = ..()
+	return ..()
+
+/// Setter for our summoner mob.
+/mob/living/simple_animal/hostile/guardian/proc/set_summoner(mob/to_who)
+	if(summoner)
+		UnregisterSignal(summoner, list(COMSIG_LIVING_ON_WABBAJACKED, COMSIG_LIVING_SHAPESHIFTED, COMSIG_LIVING_UNSHAPESHIFTED))
+
+	summoner = to_who
+	Recall(TRUE)
+	RegisterSignal(to_who, COMSIG_LIVING_ON_WABBAJACKED, .proc/on_owner_wabbajacked)
+	RegisterSignal(to_who, COMSIG_LIVING_SHAPESHIFTED, .proc/on_owner_shapeshifted)
+	RegisterSignal(to_who, COMSIG_LIVING_UNSHAPESHIFTED, .proc/on_owner_unshapeshifted)
+
+/// Signal proc for [COMSIG_LIVING_ON_WABBAJACKED], when our summoner is wabbajacked we should be alerted.
+/mob/living/simple_animal/hostile/guardian/proc/on_owner_wabbajacked(mob/living/source, mob/living/new_mob)
+	SIGNAL_HANDLER
+
+	set_summoner(new_mob)
+	to_chat(src, span_holoparasite("Your summoner has changed form!"))
+
+/// Signal proc for [COMSIG_LIVING_SHAPESHIFTED], when our summoner is shapeshifted we should change to the new mob
+/mob/living/simple_animal/hostile/guardian/proc/on_owner_shapeshifted(mob/living/source, mob/living/new_shape)
+	SIGNAL_HANDLER
+
+	set_summoner(new_shape)
+	to_chat(src, span_holoparasite("Your summoner has shapeshifted into that of a [new_shape]!"))
+
+/// Signal proc for [COMSIG_LIVING_UNSHAPESHIFTED], when our summoner unshapeshifts go back to that mob
+/mob/living/simple_animal/hostile/guardian/proc/on_owner_unshapeshifted(mob/living/source, mob/living/old_summoner)
+	SIGNAL_HANDLER
+
+	set_summoner(old_summoner)
+	to_chat(src, span_holoparasite("Your summoner has shapeshifted back into their normal form!"))
+
+// Ha, no
+/mob/living/simple_animal/hostile/guardian/wabbajack(what_to_randomize, change_flags = WABBAJACK)
+	visible_message(span_warning("[src] resists the polymorph!"))
 
 /mob/living/simple_animal/hostile/guardian/med_hud_set_health()
 	if(summoner)
@@ -401,7 +437,7 @@ GLOBAL_LIST_EMPTY(parasites) //all currently existing/living guardians
 		var/my_message = "<font color=\"[guardiancolor]\"><b><i>[src]:</i></b></font> [preliminary_message]" //add source, color source with the guardian's color
 
 		to_chat(summoner, "<span class='say'>[my_message]</span>")
-		var/list/guardians = summoner.hasparasites()
+		var/list/guardians = summoner.get_all_linked_holoparasites()
 		for(var/para in guardians)
 			to_chat(para, "<span class='say'>[my_message]</span>")
 		for(var/M in GLOB.dead_mob_list)
@@ -422,7 +458,7 @@ GLOBAL_LIST_EMPTY(parasites) //all currently existing/living guardians
 	var/my_message = "<span class='holoparasite bold'><i>[src]:</i> [preliminary_message]</span>" //add source, color source with default grey...
 
 	to_chat(src, "<span class='say'>[my_message]</span>")
-	var/list/guardians = hasparasites()
+	var/list/guardians = get_all_linked_holoparasites()
 	for(var/para in guardians)
 		var/mob/living/simple_animal/hostile/guardian/G = para
 		to_chat(G, "<span class='say'><font color=\"[G.guardiancolor]\"><b><i>[src]:</i></b></font> [preliminary_message]</span>" )
@@ -438,7 +474,7 @@ GLOBAL_LIST_EMPTY(parasites) //all currently existing/living guardians
 	set name = "Recall Guardian"
 	set category = "Guardian"
 	set desc = "Forcibly recall your guardian."
-	var/list/guardians = hasparasites()
+	var/list/guardians = get_all_linked_holoparasites()
 	for(var/para in guardians)
 		var/mob/living/simple_animal/hostile/guardian/G = para
 		G.Recall()
@@ -448,7 +484,7 @@ GLOBAL_LIST_EMPTY(parasites) //all currently existing/living guardians
 	set category = "Guardian"
 	set desc = "Re-rolls which ghost will control your Guardian. One use per Guardian."
 
-	var/list/guardians = hasparasites()
+	var/list/guardians = get_all_linked_holoparasites()
 	for(var/para in guardians)
 		var/mob/living/simple_animal/hostile/guardian/P = para
 		if(P.reset)
@@ -492,16 +528,19 @@ GLOBAL_LIST_EMPTY(parasites) //all currently existing/living guardians
 
 ////////parasite tracking/finding procs
 
-/mob/living/proc/hasparasites() //returns a list of guardians the mob is a summoner for
-	. = list()
-	for(var/P in GLOB.parasites)
-		var/mob/living/simple_animal/hostile/guardian/G = P
-		if(G.summoner == src)
-			. += G
-
-/mob/living/simple_animal/hostile/guardian/proc/hasmatchingsummoner(mob/living/simple_animal/hostile/guardian/G) //returns 1 if the summoner matches the target's summoner
-	return (istype(G) && G.summoner == summoner)
+/// Returns a list of all holoparasites that has this mob as a summoner.
+/mob/living/proc/get_all_linked_holoparasites()
+	RETURN_TYPE(/list)
+	var/list/all_parasites = list()
+	for(var/mob/living/simple_animal/hostile/guardian/stand as anything in GLOB.parasites)
+		if(stand.summoner != src)
+			continue
+		all_parasites += stand
+	return all_parasites
 
+/// Returns true if this holoparasite has the same summoner as the passed holoparasite.
+/mob/living/simple_animal/hostile/guardian/proc/hasmatchingsummoner(mob/living/simple_animal/hostile/guardian/other_guardian)
+	return istype(other_guardian) && other_guardian.summoner == summoner
 
 ////////Creation
 
@@ -528,7 +567,7 @@ GLOBAL_LIST_EMPTY(parasites) //all currently existing/living guardians
 	if(isguardian(user) && !allowguardian)
 		to_chat(user, span_holoparasite("[mob_name] chains are not allowed."))
 		return
-	var/list/guardians = user.hasparasites()
+	var/list/guardians = user.get_all_linked_holoparasites()
 	if(length(guardians) && !allowmultiple)
 		to_chat(user, span_holoparasite("You already have a [mob_name]!"))
 		return
@@ -596,14 +635,14 @@ GLOBAL_LIST_EMPTY(parasites) //all currently existing/living guardians
 		if("Gravitokinetic")
 			pickedtype = /mob/living/simple_animal/hostile/guardian/gravitokinetic
 
-	var/list/guardians = user.hasparasites()
+	var/list/guardians = user.get_all_linked_holoparasites()
 	if(length(guardians) && !allowmultiple)
 		to_chat(user, span_holoparasite("You already have a [mob_name]!") )
 		used = FALSE
 		return
 	var/mob/living/simple_animal/hostile/guardian/G = new pickedtype(user, theme)
 	G.name = mob_name
-	G.summoner = user
+	G.set_summoner(user)
 	G.key = candidate.key
 	G.mind.enslave_mind_to_creator(user)
 	G.copy_languages(user, LANGUAGE_MASTER) // make sure holoparasites speak same language as master

code/modules/mob/living/simple_animal/guardian/types/ranged.dm

@@ -122,7 +122,7 @@
 	SIGNAL_HANDLER
 	if(isliving(AM) && spawner && spawner.summoner && AM != spawner && !spawner.hasmatchingsummoner(AM))
 		to_chat(spawner.summoner, "[span_danger("<B>[AM] has crossed surveillance snare, [name].")]</B>")
-		var/list/guardians = spawner.summoner.hasparasites()
+		var/list/guardians = spawner.summoner.get_all_linked_holoparasites()
 		for(var/para in guardians)
 			to_chat(para, "[span_danger("<B>[AM] has crossed surveillance snare, [name].")]</B>")
 

code/modules/mob/living/simple_animal/hostile/mimic.dm

@@ -133,7 +133,7 @@ GLOBAL_LIST_INIT(mimic_blacklist, list(/obj/structure/table, /obj/structure/cabl
 	. = ..()
 	return . - creator
 
-/mob/living/simple_animal/hostile/mimic/copy/wabbajack()
+/mob/living/simple_animal/hostile/mimic/copy/wabbajack(what_to_randomize, change_flags = WABBAJACK)
 	visible_message(span_warning("[src] resists polymorphing into a new creature!"))
 
 /mob/living/simple_animal/hostile/mimic/copy/proc/ChangeOwner(mob/owner)

code/modules/mob/living/simple_animal/hostile/space_dragon.dm

@@ -170,8 +170,7 @@
 	fire_stream()
 
 /mob/living/simple_animal/hostile/space_dragon/death(gibbed)
-	empty_contents()
-	..()
+	. = ..()
 	add_dragon_overlay()
 	UnregisterSignal(small_sprite, COMSIG_ACTION_TRIGGER)
 
@@ -180,10 +179,6 @@
 	add_dragon_overlay()
 	RegisterSignal(small_sprite, COMSIG_ACTION_TRIGGER, .proc/add_dragon_overlay)
 
-/mob/living/simple_animal/hostile/space_dragon/wabbajack_act(mob/living/new_mob)
-	empty_contents()
-	. = ..()
-
 /**
  * Allows space dragon to choose its own name.
  *
@@ -334,18 +329,6 @@
 		return TRUE
 	return FALSE
 
-/**
- * Disperses the contents of the mob on the surrounding tiles.
- *
- * Randomly places the contents of the mob onto surrounding tiles.
- * Has a 10% chance to place on the same tile as the mob.
- */
-/mob/living/simple_animal/hostile/space_dragon/proc/empty_contents()
-	for(var/atom/movable/AM in src)
-		AM.forceMove(loc)
-		if(prob(90))
-			step(AM, pick(GLOB.alldirs))
-
 /**
  * Resets Space Dragon's status after using wing gust.
  *

code/modules/pai/shell.dm

@@ -17,7 +17,7 @@
 	if(loc != card)
 		visible_message(span_notice("[src] [resting? "lays down for a moment..." : "perks up from the ground."]"))
 
-/mob/living/silicon/pai/wabbajack()
+/mob/living/silicon/pai/wabbajack(what_to_randomize, change_flags = WABBAJACK)
 	if(length(possible_chassis) < 2)
 		return FALSE
 	var/holochassis = pick(possible_chassis - chassis)

code/modules/projectiles/ammunition/special/magic.dm

@@ -9,6 +9,19 @@
 /obj/item/ammo_casing/magic/change
 	projectile_type = /obj/projectile/magic/change
 
+/obj/item/ammo_casing/magic/change/ready_proj(atom/target, mob/living/user, quiet, zone_override = "", atom/fired_from)
+	if (!loaded_projectile)
+		return
+
+	// If we were fired by a Staff of Change, we can try to inherent their preset vars for our wabbajack
+	var/obj/item/gun/magic/staff/change/change_staff = fired_from
+	var/obj/projectile/magic/change/change_projectile = loaded_projectile
+	if(istype(change_staff) && istype(change_projectile))
+		change_projectile.set_wabbajack_effect = change_staff.preset_wabbajack_type
+		change_projectile.set_wabbajack_changeflags = change_staff.preset_wabbajack_changeflag
+
+	return ..()
+
 /obj/item/ammo_casing/magic/animate
 	projectile_type = /obj/projectile/magic/animate
 

code/modules/projectiles/guns/magic/staff.dm

@@ -6,6 +6,8 @@
 	lefthand_file = 'icons/mob/inhands/weapons/staves_lefthand.dmi'
 	righthand_file = 'icons/mob/inhands/weapons/staves_righthand.dmi'
 	item_flags = NEEDS_PERMIT | NO_MAT_REDEMPTION
+	/// Can non-magic folk use our staff?
+	/// If FALSE, only wizards or survivalists can use the staff to its full potential - If TRUE, anyone can
 	var/allow_intruder_use = FALSE
 
 /obj/item/gun/magic/staff/proc/is_wizard_or_friend(mob/user)
@@ -34,6 +36,10 @@
 	icon_state = "staffofchange"
 	inhand_icon_state = "staffofchange"
 	school = SCHOOL_TRANSMUTATION
+	/// If set, all wabbajacks this staff produces will be of this type, instead of random
+	var/preset_wabbajack_type
+	/// If set, all wabbajacks this staff produces will be of this changeflag, instead of only WABBAJACK
+	var/preset_wabbajack_changeflag
 
 /obj/item/gun/magic/staff/change/unrestricted
 	allow_intruder_use = TRUE
@@ -46,8 +52,11 @@
 
 /obj/item/gun/magic/staff/change/on_intruder_use(mob/living/user, atom/target)
 	user.dropItemToGround(src, TRUE)
-	var/randomize = pick("monkey","humanoid","animal")
-	var/mob/new_body = user.wabbajack(randomize)
+	var/wabbajack_into = preset_wabbajack_type || pick(WABBAJACK_MONKEY, WABBAJACK_HUMAN, WABBAJACK_ANIMAL)
+	var/mob/living/new_body = user.wabbajack(wabbajack_into, preset_wabbajack_changeflag)
+	if(!new_body)
+		return
+
 	balloon_alert(new_body, "wabbajack, wabbajack!")
 
 /obj/item/gun/magic/staff/animate
@@ -67,6 +76,7 @@
 	icon_state = "staffofhealing"
 	inhand_icon_state = "staffofhealing"
 	school = SCHOOL_RESTORATION
+	/// Our internal healbeam, used if an intruder (non-magic person) tries to use our staff
 	var/obj/item/gun/medbeam/healing_beam
 
 /obj/item/gun/magic/staff/healing/pickup(mob/user)
@@ -81,7 +91,7 @@
 	healing_beam.mounted = TRUE
 
 /obj/item/gun/magic/staff/healing/Destroy()
-	qdel(healing_beam)
+	QDEL_NULL(healing_beam)
 	return ..()
 
 /obj/item/gun/magic/staff/healing/unrestricted
@@ -111,18 +121,36 @@
 	recharge_rate = 2
 	no_den_usage = 1
 	school = SCHOOL_FORBIDDEN //this staff is evil. okay? it just is. look at this projectile type list. this is wrong.
-	var/allowed_projectile_types = list(/obj/projectile/magic/change, /obj/projectile/magic/animate, /obj/projectile/magic/resurrection,
-	/obj/projectile/magic/death, /obj/projectile/magic/teleport, /obj/projectile/magic/door, /obj/projectile/magic/fireball,
-	/obj/projectile/magic/spellblade, /obj/projectile/magic/arcane_barrage, /obj/projectile/magic/locker, /obj/projectile/magic/flying,
-	/obj/projectile/magic/bounty, /obj/projectile/magic/antimagic, /obj/projectile/magic/fetch, /obj/projectile/magic/sapping,
-	/obj/projectile/magic/necropotence, /obj/projectile/magic, /obj/projectile/temp/chill, /obj/projectile/magic/wipe)
+
+	/// Static list of all projectiles we can fire from our staff.
+	/// Doesn't contain all subtypes of magic projectiles, unlike what it looks like
+	var/static/list/allowed_projectile_types = list(
+		/obj/projectile/magic/animate,
+		/obj/projectile/magic/antimagic,
+		/obj/projectile/magic/arcane_barrage,
+		/obj/projectile/magic/bounty,
+		/obj/projectile/magic/change,
+		/obj/projectile/magic/death,
+		/obj/projectile/magic/door,
+		/obj/projectile/magic/fetch,
+		/obj/projectile/magic/fireball,
+		/obj/projectile/magic/flying,
+		/obj/projectile/magic/locker,
+		/obj/projectile/magic/necropotence,
+		/obj/projectile/magic/resurrection,
+		/obj/projectile/magic/sapping,
+		/obj/projectile/magic/spellblade,
+		/obj/projectile/magic/teleport,
+		/obj/projectile/magic/wipe,
+		/obj/projectile/temp/chill,
+	)
 
 /obj/item/gun/magic/staff/chaos/unrestricted
 	allow_intruder_use = TRUE
 
 /obj/item/gun/magic/staff/chaos/process_fire(atom/target, mob/living/user, message = TRUE, params = null, zone_override = "", bonus_spread = 0)
 	chambered.projectile_type = pick(allowed_projectile_types)
-	. = ..()
+	return ..()
 
 /obj/item/gun/magic/staff/chaos/on_intruder_use(mob/living/user)
 	if(!user.can_cast_magic()) // Don't let people with antimagic use the staff of chaos.
@@ -179,10 +207,10 @@
 /obj/item/gun/magic/staff/spellblade/Initialize(mapload)
 	. = ..()
 	AddComponent(/datum/component/butchering, \
-	speed = 1.5 SECONDS, \
-	effectiveness = 125, \
-	bonus_modifier = 0, \
-	butcher_sound = hitsound, \
+		speed = 1.5 SECONDS, \
+		effectiveness = 125, \
+		bonus_modifier = 0, \
+		butcher_sound = hitsound, \
 	)
 
 /obj/item/gun/magic/staff/spellblade/hit_reaction(mob/living/carbon/human/owner, atom/movable/hitby, attack_text = "the attack", final_block_chance = 0, damage = 0, attack_type = MELEE_ATTACK)

code/modules/projectiles/guns/magic/wand.dm

@@ -147,7 +147,7 @@
 	max_charges = 10 //10, 5, 5, 4
 
 /obj/item/gun/magic/wand/polymorph/zap_self(mob/living/user)
-	..() //because the user mob ceases to exists by the time wabbajack fully resolves
+	. = ..() //because the user mob ceases to exists by the time wabbajack fully resolves
 
 	user.wabbajack()
 	charges--

code/modules/projectiles/projectile/magic.dm

@@ -162,13 +162,17 @@
 	damage = 0
 	damage_type = BURN
 	nodamage = TRUE
+	/// If set, this projectile will only do a certain wabbajack effect
+	var/set_wabbajack_effect
+	/// If set, this projectile will only pass certain changeflags to wabbajack
+	var/set_wabbajack_changeflags
 
 /obj/projectile/magic/change/on_hit(atom/target)
 	. = ..()
 
 	if(isliving(target))
 		var/mob/living/victim = target
-		victim.wabbajack()
+		victim.wabbajack(set_wabbajack_effect, set_wabbajack_changeflags)
 
 	if(istype(target, /obj/machinery/hydroponics))
 		var/obj/machinery/hydroponics/plant_tray = target

code/modules/research/xenobiology/crossbreeding/_mobs.dm

@@ -21,7 +21,7 @@ Slimecrossing Mobs
 	/// If TRUE, we self-delete (remove ourselves) the next time we turn back into a human
 	var/remove_on_restore = FALSE
 
-/datum/action/cooldown/spell/shapeshift/slime_form/restore_form(mob/living/shape)
+/datum/action/cooldown/spell/shapeshift/slime_form/do_unshapeshift(mob/living/caster)
 	. = ..()
 	if(!.)
 		return

code/modules/spells/spell_types/pointed/mind_transfer.dm

@@ -19,6 +19,10 @@
 
 	/// If TRUE, we cannot mindswap into mobs with minds if they do not currently have a key / player.
 	var/target_requires_key = TRUE
+	/// If TRUE, we cannot mindswap into people without a mind.
+	/// You may be wondering "What's the point of mindswap if the target has no mind"?
+	/// Primarily for debugging - targets hit with this set to FALSE will init a mind, then do the swap.
+	var/target_requires_mind = TRUE
 	/// For how long is the caster stunned for after the spell
 	var/unconscious_amount_caster = 40 SECONDS
 	/// For how long is the victim stunned for after the spell
@@ -64,7 +68,7 @@
 	if(living_target.stat == DEAD)
 		to_chat(owner, span_warning("You don't particularly want to be dead!"))
 		return FALSE
-	if(!living_target.mind)
+	if(!living_target.mind && target_requires_mind)
 		to_chat(owner, span_warning("[living_target.p_theyve(TRUE)] doesn't appear to have a mind to swap into!"))
 		return FALSE
 	if(!living_target.key && target_requires_key)
@@ -86,6 +90,10 @@
 		if(stand.summoner)
 			to_swap = stand.summoner
 
+	// Gives the target a mind if we don't require one and they don't have one
+	if(!to_swap.mind && !target_requires_mind)
+		to_swap.mind_initialize()
+
 	var/datum/mind/mind_to_swap = to_swap.mind
 	if(to_swap.can_block_magic(antimagic_flags) \
 		|| mind_to_swap.has_antag_datum(/datum/antagonist/wizard) \

code/modules/spells/spell_types/shapeshift/_shape_status.dm

@@ -0,0 +1,236 @@
+// A status effect for having a mob temporarily (usually) change form into that of another mob.
+// When the status effect is removed, the mob is reverted back to their human form in most cases.
+// If you want a more permanent polymorph, see [/proc/wabbajack].
+/datum/status_effect/shapechange_mob
+	id = "shapechange_mob"
+	alert_type = /atom/movable/screen/alert/status_effect/shapeshifted
+	// When the mob's deleted on_remove() will handle our references
+	on_remove_on_mob_delete = TRUE
+
+	/// The caster's mob. Who has transformed into us
+	/// This reference is handled in [/proc/restore_caster], which is always called if we delete
+	var/mob/living/caster_mob
+	/// Whether we're currently undoing the change
+	var/already_restored = FALSE
+
+/datum/status_effect/shapechange_mob/on_creation(mob/living/new_owner, mob/living/caster)
+	// If any type or subtype of shapeshift mob is on the new_owner already throw an error and self-delete
+	if(locate(type) in new_owner.status_effects)
+		stack_trace("Mob shapechange status effect applied to a mob which already was shapechanged, which will definitely cause issues.")
+		qdel(src)
+		return
+
+	// No caster mob, no one to put in the mob. Self-delete
+	if(!istype(caster))
+		stack_trace("Mob shapechange status effect applied without a proper caster.")
+		qdel(src)
+		return
+
+	src.caster_mob = caster
+	return ..()
+
+/datum/status_effect/shapechange_mob/on_apply()
+	caster_mob.mind?.transfer_to(owner)
+	caster_mob.forceMove(owner)
+	caster_mob.notransform = TRUE
+	caster_mob.apply_status_effect(/datum/status_effect/grouped/stasis, STASIS_SHAPECHANGE_EFFECT)
+
+	RegisterSignal(owner, COMSIG_LIVING_PRE_WABBAJACKED, .proc/on_wabbajacked)
+	RegisterSignal(owner, COMSIG_LIVING_DEATH, .proc/on_shape_death)
+	RegisterSignal(caster_mob, COMSIG_LIVING_DEATH, .proc/on_caster_death)
+	RegisterSignal(caster_mob, COMSIG_PARENT_QDELETING, .proc/on_caster_deleted)
+
+	SEND_SIGNAL(caster_mob, COMSIG_LIVING_SHAPESHIFTED, owner)
+	return TRUE
+
+/datum/status_effect/shapechange_mob/on_remove()
+	// If the owner was straight up deleted we shouldn't restore anyone
+	// (the caster's stored in the owner's contents so if it's qdel'd so is the caster)
+	if(!QDELETED(owner))
+		restore_caster()
+
+	// Either restore_caster() or other signals should have handled this reference by now,
+	// but juuust in case make sure nothing sticks around.
+	caster_mob = null
+
+/// Signal proc for [COMSIG_LIVING_PRE_WABBAJACKED] to prevent us from being Wabbajacked and messed up.
+/datum/status_effect/shapechange_mob/proc/on_wabbajacked(mob/living/source, randomized)
+	SIGNAL_HANDLER
+
+	var/mob/living/revealed_mob = caster_mob
+	source.visible_message(span_warning("[revealed_mob] gets pulled back to their normal form!"))
+	restore_caster()
+	revealed_mob.Paralyze(10 SECONDS, ignore_canstun = TRUE)
+	return STOP_WABBAJACK
+
+/// Restores the caster back to their human form.
+/// if kill_caster_after is TRUE, the caster will have death() called on them after restoring.
+/datum/status_effect/shapechange_mob/proc/restore_caster(kill_caster_after = FALSE)
+	if(already_restored || !caster_mob)
+		return
+
+	if(QDELETED(owner))
+		CRASH("Mob shapechange effect called restore_caster while the owner was qdeleted, this shouldn't happen.")
+
+	already_restored = TRUE
+	UnregisterSignal(owner, list(COMSIG_LIVING_PRE_WABBAJACKED, COMSIG_LIVING_DEATH))
+	UnregisterSignal(caster_mob, list(COMSIG_PARENT_QDELETING, COMSIG_LIVING_DEATH))
+
+	caster_mob.forceMove(owner.loc)
+	caster_mob.notransform = FALSE
+	caster_mob.remove_status_effect(/datum/status_effect/grouped/stasis, STASIS_SHAPECHANGE_EFFECT)
+	owner.mind?.transfer_to(caster_mob)
+
+	if(kill_caster_after)
+		caster_mob.death()
+
+	after_unchange()
+	caster_mob = null
+
+	// Destroy the owner after all's said and done, this will also destroy our status effect (src)
+	// retore_caster() should never reach this point while either the owner or the effect is being qdeleted
+	qdel(owner)
+
+/// Effects done after the casting mob has reverted to their human form.
+/datum/status_effect/shapechange_mob/proc/after_unchange()
+	SHOULD_CALL_PARENT(TRUE)
+	SEND_SIGNAL(owner, COMSIG_LIVING_UNSHAPESHIFTED, caster_mob)
+
+/// Signal proc for [COMSIG_LIVING_DEATH] from our owner.
+/// If our owner mob is killed, we should revert back to normal.
+/datum/status_effect/shapechange_mob/proc/on_shape_death(datum/source, gibbed)
+	SIGNAL_HANDLER
+
+	// gibbed = deleted = nothing to restore
+	if(gibbed)
+		return
+
+	restore_caster()
+
+/// Signal proc for [COMSIG_LIVING_DEATH] from our caster.
+/// If our internal caster is killed, kill our owner, too (which causes the above signal).
+/// This should very rarely end up being called but you never know
+/datum/status_effect/shapechange_mob/proc/on_caster_death(datum/source, gibbed)
+	SIGNAL_HANDLER
+
+	// Our caster inside was gibbed, mirror the gib to our mob
+	if(gibbed)
+		owner.gib()
+
+	// Otherwise our caster died, just make our mob die
+	else
+		owner.death()
+
+/// Signal proc for [COMSIG_PARENT_QDELETING] from our caster, delete us / our owner if we get deleted
+/datum/status_effect/shapechange_mob/proc/on_caster_deleted(datum/source)
+	SIGNAL_HANDLER
+
+	caster_mob = null
+	if(QDELETED(owner))
+		return
+
+	qdel(owner)
+
+// A subtype for a shapechange sourced from a shapeshift spell.
+/datum/status_effect/shapechange_mob/from_spell
+	id = "shapechange_from_spell"
+	/// The shapechange spell that's caused our change
+	var/datum/weakref/source_weakref
+
+/datum/status_effect/shapechange_mob/from_spell/on_creation(mob/living/new_owner, mob/living/caster, datum/action/cooldown/spell/shapeshift/source_spell)
+	if(!istype(source_spell))
+		stack_trace("Mob shapechange \"from spell\" status effect applied without a source spell.")
+		qdel(src)
+		return
+
+	source_weakref = WEAKREF(source_spell)
+	return ..()
+
+/datum/status_effect/shapechange_mob/from_spell/on_apply()
+	var/datum/action/cooldown/spell/shapeshift/source_spell = source_weakref.resolve()
+	if(source_spell.owner == caster_mob)
+		// Assuming the spell is owned by the caster, give it over to the shapeshifted mob
+		// so they can actually transform back to their original form
+		source_spell.Grant(owner)
+
+		if(source_spell.convert_damage)
+			var/damage_to_apply = owner.maxHealth * ((caster_mob.maxHealth - caster_mob.health) / caster_mob.maxHealth)
+
+			owner.apply_damage(damage_to_apply, source_spell.convert_damage_type, forced = TRUE, wound_bonus = CANT_WOUND)
+			owner.blood_volume = caster_mob.blood_volume
+
+	for(var/datum/action/bodybound_action as anything in caster_mob.actions)
+		if(bodybound_action.target != caster_mob)
+			continue
+		bodybound_action.Grant(owner)
+
+	return ..()
+
+/datum/status_effect/shapechange_mob/from_spell/restore_caster(kill_caster_after)
+	var/datum/action/cooldown/spell/shapeshift/source_spell = source_weakref.resolve()
+	// The owner = owner check here is specifically for edge cases in which the owner of the spell
+	// is no longer in control of the shapeshifted mob, such as mindswapping out of a shapeshift
+	if(!QDELETED(source_spell) && source_spell.owner == owner)
+		source_spell.Grant(caster_mob)
+
+	for(var/datum/action/bodybound_action as anything in owner.actions)
+		if(bodybound_action.target != caster_mob)
+			continue
+		bodybound_action.Grant(caster_mob)
+
+	return ..()
+
+/datum/status_effect/shapechange_mob/from_spell/after_unchange()
+	. = ..()
+	var/datum/action/cooldown/spell/shapeshift/source_spell = source_weakref?.resolve()
+	if(QDELETED(source_spell) || !source_spell.convert_damage)
+		return
+
+	if(caster_mob.stat != DEAD)
+		caster_mob.revive(full_heal = TRUE, admin_revive = FALSE)
+
+		var/damage_to_apply = caster_mob.maxHealth * ((owner.maxHealth - owner.health) / owner.maxHealth)
+		caster_mob.apply_damage(damage_to_apply, source_spell.convert_damage_type, forced = TRUE, wound_bonus = CANT_WOUND)
+
+	caster_mob.blood_volume = owner.blood_volume
+
+/datum/status_effect/shapechange_mob/from_spell/on_shape_death(datum/source, gibbed)
+	var/datum/action/cooldown/spell/shapeshift/source_spell = source_weakref.resolve()
+	// If our spell dictates our wizard dies when our shape dies, we won't restore by default
+	if(!QDELETED(source_spell) && source_spell.die_with_shapeshifted_form)
+		// (But if our spell says we should revert on death anyways, we'll also do that)
+		if(source_spell.revert_on_death)
+			restore_caster(kill_caster_after = TRUE)
+		// Otherwise, we just do nothing - we dead
+		return
+
+	return ..() // Restore like normal
+
+/datum/status_effect/shapechange_mob/from_spell/on_caster_death(datum/source)
+	var/datum/action/cooldown/spell/shapeshift/source_spell = source_weakref.resolve()
+	// If our spell does not have revert_on_death, don't do anything when our caster dies
+	if(!QDELETED(source_spell) && !source_spell.revert_on_death)
+		return
+
+	return ..() // Kill our owner and revert, like normal
+
+/atom/movable/screen/alert/status_effect/shapeshifted
+	name = "Shapeshifted"
+	desc = "Your form is not your own... you're shapeshifted into another creature! \
+		A wizard could turn you back - or maybe you're stuck like this for good?"
+	icon_state = "shapeshifted"
+
+/atom/movable/screen/alert/status_effect/shapeshifted/Click(location, control, params)
+	. = ..()
+	if(!.)
+		return
+
+	var/mob/living/living_user = usr
+	if(!istype(living_user))
+		return
+
+	// Clicking the action will try to cast whatever spell shifted us in the first place
+	for(var/datum/action/cooldown/spell/shapeshift/shift_spell in living_user.actions)
+		if(istype(living_user, shift_spell.shapeshift_type))
+			shift_spell.Trigger()
+			return TRUE

code/modules/spells/spell_types/shapeshift/_shapeshift.dm

@@ -1,9 +1,20 @@
+/// Helper for checking of someone's shapeshifted currently.
+#define is_shifted(mob) mob.has_status_effect(/datum/status_effect/shapechange_mob/from_spell)
+
+/**
+ * Shapeshift spells.
+ *
+ * Allows the caster to transform to and from a different mob type.
+ */
 /datum/action/cooldown/spell/shapeshift
 	button_icon_state = "shapeshift"
 	school = SCHOOL_TRANSMUTATION
 	cooldown_time = 10 SECONDS
 
-	/// Whehter we revert to our human form on death.
+	/// Our spell's requrements before we shapeshifted. Stored on shapeshift so we can restore them after unshifting.
+	var/pre_shift_requirements
+
+	/// Whether we revert to our human form on death.
 	var/revert_on_death = TRUE
 	/// Whether we die when our shapeshifted form is killed
 	var/die_with_shapeshifted_form = TRUE
@@ -12,29 +23,35 @@
 	/// If convert damage is true, the damage type we deal when converting damage back and forth
 	var/convert_damage_type = BRUTE
 
-	/// Our chosen type
+	/// Our chosen type.
 	var/mob/living/shapeshift_type
-	/// All possible types we can become
+	/// All possible types we can become.
+	/// This should be implemented even if there is only one choice.
 	var/list/atom/possible_shapes
 
 /datum/action/cooldown/spell/shapeshift/is_valid_target(atom/cast_on)
 	return isliving(cast_on)
 
-/datum/action/cooldown/spell/shapeshift/proc/is_shifted(mob/living/cast_on)
-	return locate(/obj/shapeshift_holder) in cast_on
-
-/datum/action/cooldown/spell/shapeshift/before_cast(atom/cast_on)
+/datum/action/cooldown/spell/shapeshift/before_cast(mob/living/cast_on)
 	. = ..()
 	if(. & SPELL_CANCEL_CAST)
 		return
 
 	if(shapeshift_type)
+		// If another shapeshift spell was casted while we're already shifted, they could technically go to do_unshapeshift().
+		// However, we don't really want people casting shapeshift A to un-shapeshift from shapeshift B,
+		// as it could cause bugs or unintended behavior. So we'll just stop them here.
+		if(is_shifted(cast_on) && !is_type_in_list(cast_on, possible_shapes))
+			to_chat(cast_on, span_warning("This spell won't un-shapeshift you from this form!"))
+			return . | SPELL_CANCEL_CAST
+
 		return
 
 	if(length(possible_shapes) == 1)
 		shapeshift_type = possible_shapes[1]
 		return
 
+	// Not bothering with caching these as they're only ever shown once
 	var/list/shape_names_to_types = list()
 	var/list/shape_names_to_image = list()
 	if(!length(shape_names_to_types) || !length(shape_names_to_image))
@@ -67,24 +84,25 @@
 	cast_on.buckled?.unbuckle_mob(cast_on, force = TRUE)
 
 	var/currently_ventcrawling = (cast_on.movement_type & VENTCRAWLING)
+	var/mob/living/resulting_mob
 
 	// Do the shift back or forth
 	if(is_shifted(cast_on))
-		restore_form(cast_on)
+		resulting_mob = do_unshapeshift(cast_on)
 	else
-		do_shapeshift(cast_on)
+		resulting_mob = do_shapeshift(cast_on)
 
 	// The shift is done, let's make sure they're in a valid state now
 	// If we're not ventcrawling, we don't need to mind
-	if(!currently_ventcrawling)
+	if(!currently_ventcrawling || !resulting_mob)
 		return
 
 	// We are ventcrawling - can our new form support ventcrawling?
-	if(HAS_TRAIT(cast_on, TRAIT_VENTCRAWLER_ALWAYS) || HAS_TRAIT(cast_on, TRAIT_VENTCRAWLER_NUDE))
+	if(HAS_TRAIT(resulting_mob, TRAIT_VENTCRAWLER_ALWAYS) || HAS_TRAIT(resulting_mob, TRAIT_VENTCRAWLER_NUDE))
 		return
 
 	// Uh oh. You've shapeshifted into something that can't fit into a vent, while ventcrawling.
-	eject_from_vents(cast_on)
+	eject_from_vents(resulting_mob)
 
 /// Whenever someone shapeshifts within a vent,
 /// and enters a state in which they are no longer a ventcrawler,
@@ -107,9 +125,11 @@
 			playsound(possible_vent, 'sound/effects/reee.ogg', 75, TRUE)
 
 	priority_announce("We detected a pipe blockage around [get_area(get_turf(cast_on))], please dispatch someone to investigate.", "Central Command")
-	cast_on.death()
-	qdel(cast_on)
+	// Gib our caster, and make sure to leave nothing behind
+	// (If we leave something behind, it'll drop on the turf of the pipe, which is kinda wrong.)
+	cast_on.gib(TRUE, TRUE, TRUE)
 
+/// Callback for the radial that allows the user to choose their species.
 /datum/action/cooldown/spell/shapeshift/proc/check_menu(mob/living/caster)
 	if(QDELETED(src))
 		return FALSE
@@ -118,153 +138,43 @@
 
 	return !caster.incapacitated()
 
+/// Actually does the shapeshift, for the caster.
 /datum/action/cooldown/spell/shapeshift/proc/do_shapeshift(mob/living/caster)
-	if(is_shifted(caster))
-		to_chat(caster, span_warning("You're already shapeshifted!"))
-		CRASH("[type] called do_shapeshift while shapeshifted.")
-
-	var/mob/living/new_shape = new shapeshift_type(caster.loc)
-	var/obj/shapeshift_holder/new_shape_holder = new(new_shape, src, caster)
-
-	spell_requirements &= ~(SPELL_REQUIRES_HUMAN|SPELL_REQUIRES_WIZARD_GARB)
-
-	return new_shape_holder
-
-/datum/action/cooldown/spell/shapeshift/proc/restore_form(mob/living/caster)
-	var/obj/shapeshift_holder/current_shift = is_shifted(caster)
-	if(QDELETED(current_shift))
+	var/mob/living/new_shape = create_shapeshift_mob(caster.loc)
+	var/datum/status_effect/shapechange_mob/shapechange = new_shape.apply_status_effect(/datum/status_effect/shapechange_mob/from_spell, caster, src)
+	if(!shapechange)
+		// We failed to shift, maybe because we were already shapeshifted?
+		// Whatver the case, this shouldn't happen, so throw a stack trace.
+		to_chat(caster, span_warning("You can't shapeshift in this form!"))
+		stack_trace("[type] do_shapeshift was called when the mob was already shapeshifted (from a spell).")
 		return
 
-	var/mob/living/restored_player = current_shift.stored
+	// Make sure it's castable even in their new form.
+	pre_shift_requirements = spell_requirements
+	spell_requirements &= ~(SPELL_REQUIRES_HUMAN|SPELL_REQUIRES_WIZARD_GARB)
 
-	current_shift.restore()
-	spell_requirements = initial(spell_requirements) // Miiight mess with admin stuff.
+	return new_shape
 
-	return restored_player
+/// Actually does the un-shapeshift, from the caster. (Caster is a shapeshifted mob.)
+/datum/action/cooldown/spell/shapeshift/proc/do_unshapeshift(mob/living/caster)
+	var/datum/status_effect/shapechange_mob/shapechange = caster.has_status_effect(/datum/status_effect/shapechange_mob/from_spell)
+	if(!shapechange)
+		// We made it to do_unshapeshift without having a shapeshift status effect, this shouldn't happen.
+		to_chat(caster, span_warning("You can't un-shapeshift from this form!"))
+		stack_trace("[type] do_unshapeshift was called when the mob wasn't even shapeshifted (from a spell).")
+		return
 
-// Maybe one day, this can be a component or something
-// Until then, this is what holds data between wizard and shapeshift form whenever shapeshift is cast.
-/obj/shapeshift_holder
-	name = "Shapeshift holder"
-	resistance_flags = INDESTRUCTIBLE | LAVA_PROOF | FIRE_PROOF | ON_FIRE | UNACIDABLE | ACID_PROOF
-	var/mob/living/stored
-	var/mob/living/shape
-	var/restoring = FALSE
-	var/datum/action/cooldown/spell/shapeshift/source
+	// Restore the requirements.
+	spell_requirements = pre_shift_requirements
+	pre_shift_requirements = null
 
-/obj/shapeshift_holder/Initialize(mapload, datum/action/cooldown/spell/shapeshift/_source, mob/living/caster)
-	. = ..()
-	source = _source
-	shape = loc
-	if(!istype(shape))
-		stack_trace("shapeshift holder created outside mob/living")
-		return INITIALIZE_HINT_QDEL
-	stored = caster
+	var/mob/living/unshapeshifted_mob = shapechange.caster_mob
+	caster.remove_status_effect(/datum/status_effect/shapechange_mob/from_spell)
+	return unshapeshifted_mob
 
-	// Transfer the Shapeshift spell over, if we actually own it
-	if(source.owner == caster)
-		source.Grant(shape)
+/// Helper proc that instantiates the mob we shapeshift into.
+/// Returns an instance of a living mob. Can be overridden.
+/datum/action/cooldown/spell/shapeshift/proc/create_shapeshift_mob(atom/loc)
+	return new shapeshift_type(loc)
 
-	// Also transfer over any actions bound to them specifically - this leaves behind item actions and similar
-	// (Mindbound actions are automatically tranferred over, so we don't need to worry about it)
-	for(var/datum/action/bodybound_action as anything in caster.actions)
-		if(bodybound_action.target != caster)
-			continue
-		bodybound_action.Grant(shape)
-
-	if(stored.mind)
-		stored.mind.transfer_to(shape)
-	stored.forceMove(src)
-	stored.notransform = TRUE
-	if(source.convert_damage)
-		var/damage_percent = (stored.maxHealth - stored.health) / stored.maxHealth;
-		var/damapply = damage_percent * shape.maxHealth;
-
-		shape.apply_damage(damapply, source.convert_damage_type, forced = TRUE, wound_bonus = CANT_WOUND);
-		shape.blood_volume = stored.blood_volume;
-
-	RegisterSignal(shape, list(COMSIG_PARENT_QDELETING, COMSIG_LIVING_DEATH), .proc/shape_death)
-	RegisterSignal(stored, list(COMSIG_PARENT_QDELETING, COMSIG_LIVING_DEATH), .proc/caster_death)
-
-/obj/shapeshift_holder/Destroy()
-	// restore_form manages signal unregistering. If restoring is TRUE, we've already unregistered the signals and we're here
-	// because restore() qdel'd src.
-	if(!restoring)
-		restore()
-	stored = null
-	shape = null
-	return ..()
-
-/obj/shapeshift_holder/Moved(atom/old_loc, movement_dir, forced, list/old_locs, momentum_change = TRUE)
-	. = ..()
-	if(!restoring && !QDELETED(src))
-		restore()
-
-/obj/shapeshift_holder/handle_atom_del(atom/A)
-	if(A == stored && !restoring)
-		restore()
-
-/obj/shapeshift_holder/Exited(atom/movable/gone, direction)
-	if(stored == gone && !restoring)
-		restore()
-
-/obj/shapeshift_holder/proc/caster_death()
-	SIGNAL_HANDLER
-
-	//Something kills the stored caster through direct damage.
-	if(source.revert_on_death)
-		restore(death = TRUE)
-	else
-		shape.death()
-
-/obj/shapeshift_holder/proc/shape_death()
-	SIGNAL_HANDLER
-
-	//Shape dies.
-	if(source.die_with_shapeshifted_form)
-		if(source.revert_on_death)
-			restore(death = TRUE)
-	else
-		restore()
-
-/obj/shapeshift_holder/proc/restore(death=FALSE)
-	// Destroy() calls this proc if it hasn't been called. Unregistering here prevents multiple qdel loops
-	// when caster and shape both die at the same time.
-	UnregisterSignal(shape, list(COMSIG_PARENT_QDELETING, COMSIG_LIVING_DEATH))
-	UnregisterSignal(stored, list(COMSIG_PARENT_QDELETING, COMSIG_LIVING_DEATH))
-	restoring = TRUE
-
-	// Give Shapeshift back to the OG, if we actually own it
-	// (Shapeshift into mindswap may change the action's owner)
-	if(!QDELETED(source) && source.owner == shape)
-		source.Grant(stored)
-
-	// Also transfer their bodybound actions back
-	for(var/datum/action/bodybound_action as anything in shape.actions)
-		if(bodybound_action.target != stored)
-			continue
-		bodybound_action.Grant(stored)
-
-	stored.forceMove(shape.loc)
-	stored.notransform = FALSE
-	if(shape.mind)
-		shape.mind.transfer_to(stored)
-	if(death)
-		stored.death()
-	else if(source.convert_damage)
-		stored.revive(full_heal = TRUE, admin_revive = FALSE)
-
-		var/damage_percent = (shape.maxHealth - shape.health)/shape.maxHealth;
-		var/damapply = stored.maxHealth * damage_percent
-
-		stored.apply_damage(damapply, source.convert_damage_type, forced = TRUE, wound_bonus=CANT_WOUND)
-	if(source.convert_damage)
-		stored.blood_volume = shape.blood_volume;
-
-	// This guard is important because restore() can also be called on COMSIG_PARENT_QDELETING for shape, as well as on death.
-	// This can happen in, for example, [/proc/wabbajack] where the mob hit is qdel'd.
-	if(!QDELETED(shape))
-		QDEL_NULL(shape)
-
-	qdel(src)
-	return stored
+#undef is_shifted

code/modules/spells/spell_types/shapeshift/dragon.dm

@@ -3,6 +3,7 @@
 	name = "Dragon Form"
 	desc = "Take on the shape a lesser ash drake."
 	invocation = "RAAAAAAAAWR!"
+	invocation_type = INVOCATION_SHOUT
 	spell_requirements = NONE
 
 	possible_shapes = list(/mob/living/simple_animal/hostile/megafauna/dragon/lesser)

code/modules/spells/spell_types/shapeshift/polar_bear.dm

@@ -2,6 +2,7 @@
 	name = "Polar Bear Form"
 	desc = "Take on the shape of a polar bear."
 	invocation = "RAAAAAAAAWR!"
+	invocation_type = INVOCATION_SHOUT
 	spell_requirements = NONE
 
 	possible_shapes = list(/mob/living/simple_animal/hostile/asteroid/polarbear/lesser)

code/modules/unit_tests/create_and_destroy.dm

@@ -54,8 +54,6 @@
 	ignore += typesof(/obj/effect/pod_landingzone)
 	//We have a baseturf limit of 10, adding more than 10 baseturf helpers will kill CI, so here's a future edge case to fix.
 	ignore += typesof(/obj/effect/baseturf_helper)
-	//There's no shapeshift to hold
-	ignore += typesof(/obj/shapeshift_holder)
 	//No tauma to pass in
 	ignore += typesof(/mob/camera/imaginary_friend)
 	//No pod to gondola

code/modules/unit_tests/spell_shapeshift.dm

@@ -1,6 +1,5 @@
 /**
- * Validates that all shapeshift type spells
- * have a valid possible_shapes setup.
+ * Validates that all shapeshift type spells have a valid possible_shapes setup.
  */
 /datum/unit_test/shapeshift_spell_validity
 
@@ -18,3 +17,89 @@
 				Fail("Shapeshift spell: [shift] had an invalid / non-living shift type ([shift_type]) in their possible shapes list.")
 
 		qdel(shift)
+
+/**
+ * Validates that shapeshift spells put the mob in another mob, as they should.
+ */
+/datum/unit_test/shapeshift_spell
+
+/datum/unit_test/shapeshift_spell/Run()
+
+	var/mob/living/carbon/human/dummy = allocate(/mob/living/carbon/human)
+	dummy.mind_initialize()
+
+	for(var/spell_type in subtypesof(/datum/action/cooldown/spell/shapeshift))
+		// Test all shapeshifts as if they were on the mob's body
+		var/datum/action/cooldown/spell/shapeshift/bodybound_shift = new spell_type(dummy)
+		bodybound_shift.Grant(dummy)
+		if(LAZYLEN(bodybound_shift.possible_shapes) > 1)
+			for(var/forced_shape in bodybound_shift.possible_shapes)
+				test_spell(dummy, bodybound_shift, forced_shape)
+
+		else if(LAZYLEN(bodybound_shift.possible_shapes) == 1)
+			test_spell(dummy, bodybound_shift)
+
+		qdel(bodybound_shift)
+
+		// And test all shapeshifts as if they were on the mob's mind
+		var/datum/action/cooldown/spell/shapeshift/mindbound_shift = new spell_type(dummy.mind)
+		mindbound_shift.Grant(dummy)
+		if(LAZYLEN(mindbound_shift.possible_shapes) > 1)
+			for(var/forced_shape in mindbound_shift.possible_shapes)
+				test_spell(dummy, mindbound_shift, forced_shape)
+
+		else if(LAZYLEN(bodybound_shift.possible_shapes) == 1)
+			test_spell(dummy, mindbound_shift)
+
+		qdel(mindbound_shift)
+
+/datum/unit_test/shapeshift_spell/proc/test_spell(mob/living/carbon/human/dummy, datum/action/cooldown/spell/shapeshift/shift, forced_shape)
+	if(forced_shape)
+		shift.shapeshift_type = forced_shape
+
+	shift.next_use_time = 0
+	shift.Trigger()
+	if(!istype(dummy.loc, shift.shapeshift_type))
+		return TEST_FAIL("Shapeshift spell: [shift.name] failed to transform the dummy into the shape [initial(shift.shapeshift_type.name)].")
+
+	var/mob/living/shape = dummy.loc
+	if(!(shift in shape.actions))
+		return TEST_FAIL("Shapeshift spell: [shift.name] failed to grant the spell to the dummy's shape.")
+
+	shift.next_use_time = 0
+	shift.Trigger()
+	if(istype(dummy.loc, shift.shapeshift_type))
+		return TEST_FAIL("Shapeshift spell: [shift.name] failed to transform the dummy back into a human.")
+
+
+/**
+ * Validates that shapeshifts function properly with holoparasites.
+ */
+/datum/unit_test/shapeshift_holoparasites
+
+/datum/unit_test/shapeshift_holoparasites/Run()
+
+	var/mob/living/carbon/human/dummy = allocate(/mob/living/carbon/human)
+
+	var/datum/action/cooldown/spell/shapeshift/wizard/shift = new(dummy)
+	shift.shapeshift_type = shift.possible_shapes[1]
+	shift.Grant(dummy)
+
+	var/mob/living/simple_animal/hostile/guardian/test_stand = allocate(/mob/living/simple_animal/hostile/guardian)
+	test_stand.set_summoner(dummy)
+
+	// The stand's summoner is dummy.
+	TEST_ASSERT_EQUAL(test_stand.summoner, dummy, "Holoparasite failed to set the summoner to the correct mob.")
+
+	// Dummy casts shapeshift. The stand's summoner should become the shape the dummy is within.
+	shift.Trigger()
+	TEST_ASSERT(istype(dummy.loc, shift.shapeshift_type), "Shapeshift spell failed to transform the dummy into the shape [initial(shift.shapeshift_type.name)].")
+	TEST_ASSERT_EQUAL(test_stand.summoner, dummy.loc, "Shapeshift spell failed to transfer the holoparasite to the dummy's shape.")
+
+	// Dummy casts shapeshfit back, the stand's summoner should become the dummy again.
+	shift.next_use_time = 0
+	shift.Trigger()
+	TEST_ASSERT(!istype(dummy.loc, shift.shapeshift_type), "Shapeshift spell failed to transform the dummy back into human form.")
+	TEST_ASSERT_EQUAL(test_stand.summoner, dummy, "Shapeshift spell failed to transfer the holoparasite back to the dummy's human form.")
+
+	qdel(shift)

tgstation.dme

@@ -4343,6 +4343,7 @@
 #include "code\modules\spells\spell_types\self\stop_time.dm"
 #include "code\modules\spells\spell_types\self\summonitem.dm"
 #include "code\modules\spells\spell_types\self\voice_of_god.dm"
+#include "code\modules\spells\spell_types\shapeshift\_shape_status.dm"
 #include "code\modules\spells\spell_types\shapeshift\_shapeshift.dm"
 #include "code\modules\spells\spell_types\shapeshift\dragon.dm"
 #include "code\modules\spells\spell_types\shapeshift\polar_bear.dm"