Chaos, from Unlimited Saga.
You fight some sort of variation of him at the end of each character's game, and on most of the paths, he is just a giant bitch. HUGE BITCH, I say. The fight is just really, really long, it is hard to do more than a few points of LP damage per turn, and his last forms hit all of your characters for about 2-3 LP, and he can attack up to 5 times per turn. Oh yeah, and LP can't be restored at all, the most anyone has is 17, and there is no effective way to heal HP (which only acts as a barrier to increased LP loss.)