Sephiroth
In the Final Fantasy/Disney mash-up series Kingdom Hearts, Sephiroth is truly the worst of both worlds, especially when you have the option to face him in the first game. For starters, you have to face him by yourself with no support from your team. Then there’s the fact that he’s insanely nasty, with lightning-quick timing, stacks on stacks on stacks of health, plus a sword that’s literally as long as three swords (and hits as hard as ten). Fighting him was optional, but not if you wanted bragging rights with the other JRPG/Disney crossover crowd.