diff --git a/code/datums/brain_damage/split_personality.dm b/code/datums/brain_damage/split_personality.dm
new file mode 100644
index 0000000000..a1284319f1
--- /dev/null
+++ b/code/datums/brain_damage/split_personality.dm
@@ -0,0 +1,224 @@
+#define OWNER 0
+#define STRANGER 1
+
+/datum/brain_trauma/severe/split_personality
+	name = "Split Personality"
+	desc = "Patient's brain is split into two personalities, which randomly switch control of the body."
+	scan_desc = "complete lobe separation"
+	gain_text = "<span class='warning'>You feel like your mind was split in two.</span>"
+	lose_text = "<span class='notice'>You feel alone again.</span>"
+	var/current_controller = OWNER
+	var/initialized = FALSE //to prevent personalities deleting themselves while we wait for ghosts
+	var/mob/living/split_personality/stranger_backseat //there's two so they can swap without overwriting
+	var/mob/living/split_personality/owner_backseat
+
+/datum/brain_trauma/severe/split_personality/on_gain()
+	var/mob/living/M = owner
+	if(M.stat == DEAD)	//No use assigning people to a corpse
+		qdel(src)
+		return
+	..()
+	make_backseats()
+	get_ghost()
+
+/datum/brain_trauma/severe/split_personality/proc/make_backseats()
+	stranger_backseat = new(owner, src)
+	owner_backseat = new(owner, src)
+
+/datum/brain_trauma/severe/split_personality/proc/get_ghost()
+	set waitfor = FALSE
+	var/list/mob/dead/observer/candidates = pollCandidatesForMob("Do you want to play as [owner]'s split personality?", ROLE_PAI, null, null, 75, stranger_backseat, POLL_IGNORE_SPLITPERSONALITY)
+	if(LAZYLEN(candidates))
+		var/mob/dead/observer/C = pick(candidates)
+		C.transfer_ckey(stranger_backseat, FALSE)
+		log_game("[key_name(stranger_backseat)] became [key_name(owner)]'s split personality.")
+		message_admins("[ADMIN_LOOKUPFLW(stranger_backseat)] became [ADMIN_LOOKUPFLW(owner)]'s split personality.")
+	else
+		qdel(src)
+
+/datum/brain_trauma/severe/split_personality/on_life()
+	if(owner.stat == DEAD)
+		if(current_controller != OWNER)
+			switch_personalities()
+		qdel(src)
+	else if(prob(3))
+		switch_personalities()
+	..()
+
+/datum/brain_trauma/severe/split_personality/on_lose()
+	if(current_controller != OWNER) //it would be funny to cure a guy only to be left with the other personality, but it seems too cruel
+		switch_personalities()
+	QDEL_NULL(stranger_backseat)
+	QDEL_NULL(owner_backseat)
+	..()
+
+/datum/brain_trauma/severe/split_personality/proc/switch_personalities()
+	if(QDELETED(owner) || owner.stat == DEAD || QDELETED(stranger_backseat) || QDELETED(owner_backseat))
+		return
+
+	var/mob/living/split_personality/current_backseat
+	var/mob/living/split_personality/free_backseat
+	if(current_controller == OWNER)
+		current_backseat = stranger_backseat
+		free_backseat = owner_backseat
+	else
+		current_backseat = owner_backseat
+		free_backseat = stranger_backseat
+
+	log_game("[key_name(current_backseat)] assumed control of [key_name(owner)] due to [src]. (Original owner: [current_controller == OWNER ? owner.key : current_backseat.key])")
+	to_chat(owner, "<span class='userdanger'>You feel your control being taken away... your other personality is in charge now!</span>")
+	to_chat(current_backseat, "<span class='userdanger'>You manage to take control of your body!</span>")
+
+	//Body to backseat
+
+	var/h2b_id = owner.computer_id
+	var/h2b_ip= owner.lastKnownIP
+	owner.computer_id = null
+	owner.lastKnownIP = null
+
+	free_backseat.ckey = owner.ckey
+
+	free_backseat.name = owner.name
+
+	if(owner.mind)
+		free_backseat.mind = owner.mind
+
+	if(!free_backseat.computer_id)
+		free_backseat.computer_id = h2b_id
+
+	if(!free_backseat.lastKnownIP)
+		free_backseat.lastKnownIP = h2b_ip
+
+	//Backseat to body
+
+	var/s2h_id = current_backseat.computer_id
+	var/s2h_ip= current_backseat.lastKnownIP
+	current_backseat.computer_id = null
+	current_backseat.lastKnownIP = null
+
+	owner.ckey = current_backseat.ckey
+	owner.mind = current_backseat.mind
+
+	if(!owner.computer_id)
+		owner.computer_id = s2h_id
+
+	if(!owner.lastKnownIP)
+		owner.lastKnownIP = s2h_ip
+
+	current_controller = !current_controller
+
+
+/mob/living/split_personality
+	name = "split personality"
+	real_name = "unknown conscience"
+	var/mob/living/carbon/body
+	var/datum/brain_trauma/severe/split_personality/trauma
+
+/mob/living/split_personality/Initialize(mapload, _trauma)
+	if(iscarbon(loc))
+		body = loc
+		name = body.real_name
+		real_name = body.real_name
+		trauma = _trauma
+	return ..()
+
+/mob/living/split_personality/Life()
+	if(QDELETED(body))
+		qdel(src) //in case trauma deletion doesn't already do it
+
+	if((body.stat == DEAD && trauma.owner_backseat == src))
+		trauma.switch_personalities()
+		qdel(trauma)
+
+	//if one of the two ghosts, the other one stays permanently
+	if(!body.client && trauma.initialized)
+		trauma.switch_personalities()
+		qdel(trauma)
+
+	..()
+
+/mob/living/split_personality/Login()
+	..()
+	to_chat(src, "<span class='notice'>As a split personality, you cannot do anything but observe. However, you will eventually gain control of your body, switching places with the current personality.</span>")
+	to_chat(src, "<span class='warning'><b>Do not commit suicide or put the body in a deadly position. Behave like you care about it as much as the owner.</b></span>")
+
+/mob/living/split_personality/say(message, bubble_type, var/list/spans = list(), sanitize = TRUE, datum/language/language = null, ignore_spam = FALSE, forced = null)
+	to_chat(src, "<span class='warning'>You cannot speak, your other self is controlling your body!</span>")
+	return FALSE
+
+/mob/living/split_personality/emote(act, m_type = null, message = null, intentional = FALSE)
+	return
+
+///////////////BRAINWASHING////////////////////
+
+/datum/brain_trauma/severe/split_personality/brainwashing
+	name = "Split Personality"
+	desc = "Patient's brain is split into two personalities, which randomly switch control of the body."
+	scan_desc = "complete lobe separation"
+	gain_text = ""
+	lose_text = "<span class='notice'>You are free of your brainwashing.</span>"
+	can_gain = FALSE
+	var/codeword
+	var/objective
+
+/datum/brain_trauma/severe/split_personality/brainwashing/New(obj/item/organ/brain/B, _permanent, _codeword, _objective)
+	..()
+	if(_codeword)
+		codeword = _codeword
+	else
+		codeword = pick(strings("ion_laws.json", "ionabstract")\
+			| strings("ion_laws.json", "ionobjects")\
+			| strings("ion_laws.json", "ionadjectives")\
+			| strings("ion_laws.json", "ionthreats")\
+			| strings("ion_laws.json", "ionfood")\
+			| strings("ion_laws.json", "iondrinks"))
+
+/datum/brain_trauma/severe/split_personality/brainwashing/on_gain()
+	..()
+	var/mob/living/split_personality/traitor/traitor_backseat = stranger_backseat
+	traitor_backseat.codeword = codeword
+	traitor_backseat.objective = objective
+
+/datum/brain_trauma/severe/split_personality/brainwashing/make_backseats()
+	stranger_backseat = new /mob/living/split_personality/traitor(owner, src, codeword, objective)
+	owner_backseat = new(owner, src)
+
+/datum/brain_trauma/severe/split_personality/brainwashing/get_ghost()
+	set waitfor = FALSE
+	var/list/mob/dead/observer/candidates = pollCandidatesForMob("Do you want to play as [owner]'s brainwashed mind?", null, null, null, 75, stranger_backseat)
+	if(LAZYLEN(candidates))
+		var/mob/dead/observer/C = pick(candidates)
+		C.transfer_ckey(stranger_backseat, FALSE)
+	else
+		qdel(src)
+
+/datum/brain_trauma/severe/split_personality/brainwashing/on_life()
+	return //no random switching
+
+/datum/brain_trauma/severe/split_personality/brainwashing/handle_hearing(datum/source, list/hearing_args)
+	if(HAS_TRAIT(owner, TRAIT_DEAF) || owner == hearing_args[HEARING_SPEAKER])
+		return
+	var/message = hearing_args[HEARING_RAW_MESSAGE]
+	if(findtext(message, codeword))
+		hearing_args[HEARING_RAW_MESSAGE] = replacetext(message, codeword, "<span class='warning'>[codeword]</span>")
+		addtimer(CALLBACK(src, /datum/brain_trauma/severe/split_personality.proc/switch_personalities), 10)
+
+/datum/brain_trauma/severe/split_personality/brainwashing/handle_speech(datum/source, list/speech_args)
+	if(findtext(speech_args[SPEECH_MESSAGE], codeword))
+		speech_args[SPEECH_MESSAGE] = "" //oh hey did you want to tell people about the secret word to bring you back?
+
+/mob/living/split_personality/traitor
+	name = "split personality"
+	real_name = "unknown conscience"
+	var/objective
+	var/codeword
+
+/mob/living/split_personality/traitor/Login()
+	..()
+	to_chat(src, "<span class='notice'>As a brainwashed personality, you cannot do anything yet but observe. However, you may gain control of your body if you hear the special codeword, switching places with the current personality.</span>")
+	to_chat(src, "<span class='notice'>Your activation codeword is: <b>[codeword]</b></span>")
+	if(objective)
+		to_chat(src, "<span class='notice'>Your master left you an objective: <b>[objective]</b>. Follow it at all costs when in control.</span>")
+
+#undef OWNER
+#undef STRANGER