Mot from Shin Megami Tensei Nocturne is the first one that comes to mind. His ability to make press turns out of nothing can be infuriating.
Lucifer from Devil Survivor is also pretty hard. You literally need almost everything maxed out, he has three stages, and if you miss once you just lose. Minotaur from SMT: IV is really hard for being one of the first bosses you fight.