diff --git a/code/__DEFINES/DNA.dm b/code/__DEFINES/DNA.dm
index d305bfa69c..62c3c1f8db 100644
--- a/code/__DEFINES/DNA.dm
+++ b/code/__DEFINES/DNA.dm
@@ -127,6 +127,7 @@
 #define TOXINLOVER		24
 #define DIGITIGRADE		25	//Uses weird leg sprites. Optional for Lizards, required for ashwalkers. Don't give it to other races unless you make sprites for this (see human_parts_greyscale.dmi)
 #define NO_UNDERWEAR	26
+<<<<<<< HEAD
 #define MUTCOLORS2		27
 #define MUTCOLORS3		28
 #define NOLIVER 		29
@@ -134,3 +135,8 @@
 //citadel code
 #define NOAROUSAL		29//Stops all arousal effects
 #define NOGENITALS		30//Cannot create, use, or otherwise have genitals
+=======
+#define NOLIVER			27
+#define NOSTOMACH		28
+#define NO_DNA_COPY     29
+>>>>>>> ed43a09... Prevents the creation of Shadowzombiechangelings (#30681)
diff --git a/code/datums/diseases/dna_spread.dm b/code/datums/diseases/dna_spread.dm
index 2b77885359..987889ce44 100644
--- a/code/datums/diseases/dna_spread.dm
+++ b/code/datums/diseases/dna_spread.dm
@@ -1,3 +1,4 @@
+<<<<<<< HEAD
 /datum/disease/dnaspread
 	name = "Space Retrovirus"
 	max_stages = 4
@@ -71,4 +72,80 @@
 		affected_mob.domutcheck()
 
 		to_chat(affected_mob, "<span class='notice'>You feel more like yourself.</span>")
-	return ..()
\ No newline at end of file
+	return ..()
+=======
+/datum/disease/dnaspread
+	name = "Space Retrovirus"
+	max_stages = 4
+	spread_text = "On contact"
+	spread_flags = CONTACT_GENERAL
+	cure_text = "Mutadone"
+	cures = list("mutadone")
+	disease_flags = CAN_CARRY|CAN_RESIST|CURABLE
+	agent = "S4E1 retrovirus"
+	viable_mobtypes = list(/mob/living/carbon/human)
+	var/datum/dna/original_dna = null
+	var/transformed = 0
+	desc = "This disease transplants the genetic code of the initial vector into new hosts."
+	severity = MEDIUM
+
+
+/datum/disease/dnaspread/stage_act()
+	..()
+	if(!affected_mob.dna)
+		cure()
+	if((NOTRANSSTING in affected_mob.dna.species.species_traits) || (NO_DNA_COPY in affected_mob.dna.species.species_traits)) //Only species that can be spread by transformation sting can be spread by the retrovirus
+		cure()
+
+	if(!strain_data["dna"])
+		//Absorbs the target DNA.
+		strain_data["dna"] = new affected_mob.dna.type
+		affected_mob.dna.copy_dna(strain_data["dna"])
+		carrier = TRUE
+		stage = 4
+		return
+
+	switch(stage)
+		if(2 || 3) //Pretend to be a cold and give time to spread.
+			if(prob(8))
+				affected_mob.emote("sneeze")
+			if(prob(8))
+				affected_mob.emote("cough")
+			if(prob(1))
+				to_chat(affected_mob, "<span class='danger'>Your muscles ache.</span>")
+				if(prob(20))
+					affected_mob.take_bodypart_damage(1)
+			if(prob(1))
+				to_chat(affected_mob, "<span class='danger'>Your stomach hurts.</span>")
+				if(prob(20))
+					affected_mob.adjustToxLoss(2)
+					affected_mob.updatehealth()
+		if(4)
+			if(!transformed && !carrier)
+				//Save original dna for when the disease is cured.
+				original_dna = new affected_mob.dna.type
+				affected_mob.dna.copy_dna(original_dna)
+
+				to_chat(affected_mob, "<span class='danger'>You don't feel like yourself..</span>")
+				var/datum/dna/transform_dna = strain_data["dna"]
+
+				transform_dna.transfer_identity(affected_mob, transfer_SE = 1)
+				affected_mob.real_name = affected_mob.dna.real_name
+				affected_mob.updateappearance(mutcolor_update=1)
+				affected_mob.domutcheck()
+
+				transformed = 1
+				carrier = 1 //Just chill out at stage 4
+
+	return
+
+/datum/disease/dnaspread/Destroy()
+	if (original_dna && transformed && affected_mob)
+		original_dna.transfer_identity(affected_mob, transfer_SE = 1)
+		affected_mob.real_name = affected_mob.dna.real_name
+		affected_mob.updateappearance(mutcolor_update=1)
+		affected_mob.domutcheck()
+
+		to_chat(affected_mob, "<span class='notice'>You feel more like yourself.</span>")
+	return ..()
+>>>>>>> ed43a09... Prevents the creation of Shadowzombiechangelings (#30681)
diff --git a/code/game/gamemodes/changeling/changeling.dm b/code/game/gamemodes/changeling/changeling.dm
index 14126c69f3..e67ac26d3a 100644
--- a/code/game/gamemodes/changeling/changeling.dm
+++ b/code/game/gamemodes/changeling/changeling.dm
@@ -340,6 +340,10 @@ GLOBAL_LIST_INIT(slot2type, list("head" = /obj/item/clothing/head/changeling, "w
 			return
 	if(!target)
 		return
+	if(NO_DNA_COPY in target.dna.species.species_traits)
+		if(verbose)
+			to_chat(user, "<span class='warning'>[target] is not compatible with our biology.</span>")
+		return
 	if((target.disabilities & NOCLONE) || (target.disabilities & HUSK))
 		if(verbose)
 			to_chat(user, "<span class='warning'>DNA of [target] is ruined beyond usability!</span>")
diff --git a/code/modules/mob/living/carbon/human/species_types/shadowpeople.dm b/code/modules/mob/living/carbon/human/species_types/shadowpeople.dm
index 636c2b7890..5c635fb870 100644
--- a/code/modules/mob/living/carbon/human/species_types/shadowpeople.dm
+++ b/code/modules/mob/living/carbon/human/species_types/shadowpeople.dm
@@ -30,7 +30,7 @@
 	burnmod = 1.5
 	blacklisted = TRUE
 	no_equip = list(slot_wear_mask, slot_wear_suit, slot_gloves, slot_shoes, slot_w_uniform, slot_s_store)
-	species_traits = list(NOBREATH,RESISTCOLD,RESISTPRESSURE,NOGUNS,NOBLOOD,RADIMMUNE,VIRUSIMMUNE,PIERCEIMMUNE,NODISMEMBER,NO_UNDERWEAR,NOHUNGER)
+	species_traits = list(NOBREATH,RESISTCOLD,RESISTPRESSURE,NOGUNS,NOBLOOD,RADIMMUNE,VIRUSIMMUNE,PIERCEIMMUNE,NODISMEMBER,NO_UNDERWEAR,NOHUNGER,NO_DNA_COPY,NOTRANSSTING)
 	mutanteyes = /obj/item/organ/eyes/night_vision/nightmare
 	var/obj/effect/proc_holder/spell/targeted/shadowwalk/shadowwalk
 
diff --git a/code/modules/mob/living/carbon/human/species_types/synths.dm b/code/modules/mob/living/carbon/human/species_types/synths.dm
index c6fba442de..6e24ce78ab 100644
--- a/code/modules/mob/living/carbon/human/species_types/synths.dm
+++ b/code/modules/mob/living/carbon/human/species_types/synths.dm
@@ -1,3 +1,4 @@
+<<<<<<< HEAD
 /datum/species/synth
 	name = "Synth" //inherited from the real species, for health scanners and things
 	id = "synth"
@@ -118,4 +119,126 @@
 		else
 			return ..()
 	else
+=======
+/datum/species/synth
+	name = "Synth" //inherited from the real species, for health scanners and things
+	id = "synth"
+	say_mod = "beep boops" //inherited from a user's real species
+	sexes = 0
+	species_traits = list(NOTRANSSTING,NOBREATH,VIRUSIMMUNE,NODISMEMBER,NOHUNGER) //all of these + whatever we inherit from the real species
+	dangerous_existence = 1
+	blacklisted = 1
+	meat = null
+	damage_overlay_type = "synth"
+	limbs_id = "synth"
+	var/list/initial_species_traits = list(NOTRANSSTING,NOBREATH,VIRUSIMMUNE,NODISMEMBER,NOHUNGER,NO_DNA_COPY) //for getting these values back for assume_disguise()
+	var/disguise_fail_health = 75 //When their health gets to this level their synthflesh partially falls off
+	var/datum/species/fake_species = null //a species to do most of our work for us, unless we're damaged
+
+/datum/species/synth/military
+	name = "Military Synth"
+	id = "military_synth"
+	armor = 25
+	punchdamagelow = 10
+	punchdamagehigh = 19
+	punchstunthreshold = 14 //about 50% chance to stun
+	disguise_fail_health = 50
+
+/datum/species/synth/on_species_gain(mob/living/carbon/human/H, datum/species/old_species)
+	..()
+	assume_disguise(old_species, H)
+
+/datum/species/synth/handle_chemicals(datum/reagent/chem, mob/living/carbon/human/H)
+	if(chem.id == "synthflesh")
+		chem.reaction_mob(H, TOUCH, 2 ,0) //heal a little
+		H.reagents.remove_reagent(chem.id, REAGENTS_METABOLISM)
+		return 1
+	else
+		return ..()
+
+
+/datum/species/synth/proc/assume_disguise(datum/species/S, mob/living/carbon/human/H)
+	if(S && !istype(S, type))
+		name = S.name
+		say_mod = S.say_mod
+		sexes = S.sexes
+		species_traits = initial_species_traits.Copy()
+		species_traits.Add(S.species_traits)
+		attack_verb = S.attack_verb
+		attack_sound = S.attack_sound
+		miss_sound = S.miss_sound
+		meat = S.meat
+		mutant_bodyparts = S.mutant_bodyparts.Copy()
+		mutant_organs = S.mutant_organs.Copy()
+		default_features = S.default_features.Copy()
+		nojumpsuit = S.nojumpsuit
+		no_equip = S.no_equip.Copy()
+		limbs_id = S.limbs_id
+		use_skintones = S.use_skintones
+		fixed_mut_color = S.fixed_mut_color
+		hair_color = S.hair_color
+		fake_species = new S.type
+	else
+		name = initial(name)
+		say_mod = initial(say_mod)
+		species_traits = initial_species_traits.Copy()
+		attack_verb = initial(attack_verb)
+		attack_sound = initial(attack_sound)
+		miss_sound = initial(miss_sound)
+		mutant_bodyparts = list()
+		default_features = list()
+		nojumpsuit = initial(nojumpsuit)
+		no_equip = list()
+		qdel(fake_species)
+		fake_species = null
+		meat = initial(meat)
+		limbs_id = "synth"
+		use_skintones = 0
+		sexes = 0
+		fixed_mut_color = ""
+		hair_color = ""
+
+	for(var/X in H.bodyparts) //propagates the damage_overlay changes
+		var/obj/item/bodypart/BP = X
+		BP.update_limb()
+	H.update_body_parts() //to update limb icon cache with the new damage overlays
+
+//Proc redirects:
+//Passing procs onto the fake_species, to ensure we look as much like them as possible
+
+/datum/species/synth/handle_hair(mob/living/carbon/human/H, forced_colour)
+	if(fake_species)
+		fake_species.handle_hair(H, forced_colour)
+	else
+		return ..()
+
+
+/datum/species/synth/handle_body(mob/living/carbon/human/H)
+	if(fake_species)
+		fake_species.handle_body(H)
+	else
+		return ..()
+
+
+/datum/species/synth/handle_mutant_bodyparts(mob/living/carbon/human/H, forced_colour)
+	if(fake_species)
+		fake_species.handle_body(H,forced_colour)
+	else
+		return ..()
+
+
+/datum/species/synth/get_spans()
+	if(fake_species)
+		return fake_species.get_spans()
+	return list()
+
+
+/datum/species/synth/handle_speech(message, mob/living/carbon/human/H)
+	if(H.health > disguise_fail_health)
+		if(fake_species)
+			return fake_species.handle_speech(message,H)
+		else
+			return ..()
+	else
+>>>>>>> ed43a09... Prevents the creation of Shadowzombiechangelings (#30681)
 		return ..()
diff --git a/code/modules/mob/living/carbon/human/species_types/zombies.dm b/code/modules/mob/living/carbon/human/species_types/zombies.dm
index d11f71212c..7c25b4d3cb 100644
--- a/code/modules/mob/living/carbon/human/species_types/zombies.dm
+++ b/code/modules/mob/living/carbon/human/species_types/zombies.dm
@@ -6,7 +6,7 @@
 	sexes = 0
 	blacklisted = 1
 	meat = /obj/item/reagent_containers/food/snacks/meat/slab/human/mutant/zombie
-	species_traits = list(NOBREATH,RESISTCOLD,RESISTPRESSURE,NOBLOOD,RADIMMUNE,NOZOMBIE,EASYDISMEMBER,EASYLIMBATTACHMENT)
+	species_traits = list(NOBREATH,RESISTCOLD,RESISTPRESSURE,NOBLOOD,RADIMMUNE,NOZOMBIE,EASYDISMEMBER,EASYLIMBATTACHMENT,NOTRANSSTING)
 	mutant_organs = list(/obj/item/organ/tongue/zombie)
 	var/static/list/spooks = list('sound/hallucinations/growl1.ogg','sound/hallucinations/growl2.ogg','sound/hallucinations/growl3.ogg','sound/hallucinations/veryfar_noise.ogg','sound/hallucinations/wail.ogg')
 	disliked_food = NONE