Wily from MM7 was nothing, but Wily from MM4 was a bitch! I was using Ring Man on him, exchange of one ring for one bar of damage. He had one bar left and I had one ring left and.....I missed. It pissed me off to oblivion. I've never had the chance to beat that game again since (this was like back in '95 I wanna say)
All the other MMs were easy, but that Wily was hard as hell!