The cheapest boss so that I've met so far is the end boss of Conan.
First you engage him in fairly straightforward one on one combat, but after taking down his health bar he jumps into the center of the room and starts spinning around, shooting out tentacles that you have to avoid while trying to move a big wheel that when turned steals one of your magic powers. This is followed by more one on one combat, but now the baddie has new moves. Each time his healthbar gets knocked down you've got to avoid his tentacles, that get harder to dodge each time. I liked the game up to that point... after dying for the nth time I put the game away and haven't looked back yet.
The Nightmare boss of Devil May Cry was also a gamebreaker for me. I just couldn't get past that bugger and still haven't finished DMC, even though I've played through DMC3 and DMC4 on a variety of difficulty levels...
First you engage him in fairly straightforward one on one combat, but after taking down his health bar he jumps into the center of the room and starts spinning around, shooting out tentacles that you have to avoid while trying to move a big wheel that when turned steals one of your magic powers. This is followed by more one on one combat, but now the baddie has new moves. Each time his healthbar gets knocked down you've got to avoid his tentacles, that get harder to dodge each time. I liked the game up to that point... after dying for the nth time I put the game away and haven't looked back yet.
The Nightmare boss of Devil May Cry was also a gamebreaker for me. I just couldn't get past that bugger and still haven't finished DMC, even though I've played through DMC3 and DMC4 on a variety of difficulty levels...