Most frustrating, cheapest video game boss you ever beaten?

Nemesis from RE3, this motherfucker was just incredible cheap. HE was chasing you throughout the whole game, takes a tons of ammo to take him down but he just keeps resurrecting. Also he's very fast and his attacks are fucking deadly, you don't wanna be in close range with him, because movements in RE1-3 are very clumsy and it takes time to get used to controls.