that you could only beat using cheats, a guide, or advice from someone who already beat him.
I have four on my mind:
Ruby Weapon (FF7, holy christ everyone knows the amount of preparation necessary for this dude.)
The End (MGS3, I fought him 15 times. That's 15 times of him dragging my ass to a shed, and each try took an hour at least.)
Lu Bu (Dynasty Warriors, I was never able to beat him, really. His ass is too hard.)
Mike Tyson (Punch Out!, my brother, who is a professional boxer with catlike reflexes, beat him way back then when I cried continuously every time he knocked me out.)
EDIT: this should've been in the general gaming section. my mistake.