Janus: The Persona
Janus: The Persona is a fanmade game set in the New World of Darkness about people experiencing a Doctor Jekyll and Mister Hyde-style situation.
Not only do you have to deal with the usual supernatural shenanigans, but you also have to consider your Id that somehow became sentient and eggs you on to do terrible life choices. But hey, you get a few nifty powers in return, so it can't be *that* bad, right?