As in TV cartoons.
Me? I'd say it's the Lich from Adventure Time. I've never seen a cartoon villain as fucked up as him. Committing atrocities like possessing Princess Bubblegum, killing Finn's idol Billy and using his flayed skin as a disguise, and of course, trying to end all life.
How about yours? (Make sure they're actually listed as a CM by TV Tropes)