Split Personality [-15] is a mundane mental disadvantage with a self-control roll, a fairly cinematic version of the real condition of “
dissociative identity disorder.” You have two (or more) distinct personalities, with different mental traits, who interpret their memories differently, and may use separate names. This disadvantage first appeared at
GURPS 1e, although its mechanics have changed significantly, and older-edition Split Personalities aren’t always exactly convertible to 4e.
To build these personalities, create a “package” of mental disadvantages and quirks, and at the GM’s option, variations in IQ, Per, Will and mental advantages. Your different personalities have
different packages; only one is available at a time, and you only have to pay for one package. This is because you don’t have any control over which personality you use: in a stressful situation, you need to make a self-control roll, or change to a different personality. This can’t happen more than once per game hour, and if there are several possibilities, the GM gets to select a personality, or roll randomly.
Their total cost of each package must be the same, and the GM gets to enforce limits on disadvantages, on the number of quirks and/or perks you have at a time, and any other character generation rules they feel are relevant. Everything that isn’t in a package, including physical traits and skills, is the same for all the personalities, although they are at liberty to not use skills, and pretend their other traits are lower (or higher, with Delusions, Overconfidence, etc.) than they really are. They can also have abilities that are only accessible to one personality: there’s a specific Accessibility value of -40% for that case.
Note that the number of personalities you have doesn’t affect the cost. This leaves you free to create new personalities in play if the GM will let you; I’d restrict it to after traumatic events, such as serious injuries and failed fright checks. All of your personalities are a bit shallow and unnatural, which gives you -1 to all reaction rolls. Anyone who witnesses you changing personality is likely to feel you’re seriously mentally ill, and react at -3 thereafter.
Split Personality is a plausible Secret Disadvantage, and an Evil Twin is readily mistaken for it. Personality Change is a Basic Set quirk-level version. Characters who have Shapeshifting with the Uncontrollable limitation may well have a linked Split Personality as well. Unethical
Bio-Tech can cause it, and
High-Tech psychiatric medication can suppress it, although it’s always grounds for refusing gun licenses according to
Pulp Guns. Reich-5’s unfortunate Mules suffer it in
Infinite Worlds, which is probably worse than the Tsarevich Curse version from
Worlds of Horror.
Power-Ups 2 makes Split Personality a valid Controllable Disadvantage perk, and
Power-Ups 6 has the interesting Residual Personality quirk for shape-changers.
A
Psi-Tech Mind-Transfer Machine can fail this way, and it’s a possible result of
Psionic Powers crippling, or
Steampunk Shocking Revelations. Some
Supers characters have a Split Personality for their civilian identity, but a formal diagnosis forbids a Concealed Carry Permit most places, in the realism of
Tactical Shooting.
Thaumatology allows this disadvantage as a consequence of spiritual possession, and
Ultra-Tech does the same for personality downloading.
A full case of Split Personality is character-defining, and fits much better into some genres, such as horror or illuminated games, than action-adventure. The only case I’ve seen in play was actually in
Champions, but had similar mechanics: a descendent of Aramis, one of the Three Musketeers, was sometimes possessed by his spirit. This was made more complicated by the descendent being female, and Aramis’ lack of interest in learning about the modern world. Eventually, the two personalities merged.
Has this disadvantage entertained in your games?