The Jealous Bass from Mother 3.
I was stuck on this guy for a good-week, trying out several-tactics. Eventually I just snapped, fired 15-Pencil Rockets, and spammed the shit out of PK Love.
Mega Gideon from Scott Pilgrim vs. The World: The GAME. I was severely underleveled, and all my stats were under 30. I was doing about 12-Damage every hit and I was taking about 40-Damage and was stunned for about 5-seconds every time. It was a nightmare. Until, after, like, 5-days I found the Power of Love stuck in the cloud just next to the battle-arena. I can't beleive I didn't see it the first couple of hundred times.
Brock from Dead Rising.
I swear, when he wasn't beating me up on the tank, he was knocking me into the nearby crowd of zombies to watch me being slowly eaten alive. God, he was an absoloute *****.