Insanity

[Colder]

Probably way too late by now, but if you ever plan to do something like this again, or remake or whatever, the new Gundam show, Gundam 00 springs to mind, specifically Allelujah/Hallelujah. Allelujah has an alternate personality, Hallelujah whom he often converses with, and who regularly causes him to suffer flashbacks to the worst day of his life (day he murdered a whole ship full of his friends). Hallelujah himself is a complete psycho, with a frightening smile, and a tendency towards homicidal rage and sadistic humour; at one point he melts an opponents suit slowly, laughing and mocking Allelujah the entire time. Another time he talks Allelujah into murdering a building full of kids. One of the show's main villain, Ali also has his moments.

Full Metal Panic also comes to mind; Gates, Gauron, and minor villain Takama are all pretty sick (with Gates-who actually meets all the clinical requirements for psychopathy-taking the cake). As my one friend put it, you can feel the crazy coming off of Gauron and Gates.

Hope this is somehow useful, even this late.

[AniMaya]

I don't think anybody has mentioned it, but... Deathnote? The last three episodes are the best, cause Light goes crazy. :3