Sephiroth in KH2. I haven't versed him in KH1 before... but man, if あなた don't level up, he is annoyingly difficult to fight xP But once levelled up it's quite easy I guess.
Also some FFX bosses were pretty hard (can't remember names off the 上, ページのトップへ of my head) but man I would spend hours on this one (I had no fast internet back then to check for solutions...) and I would be attacking it, it was almost dead, then right when it's almost dead after attacking it, it completely restored its health -__- But yeah, あなた need strategy and to be levelled up in FFX otherwise you're screwed xP
Easy? Hmm... too many to mention? I dunno, I guess the final battles for the Spyro games were always quite easy, but that's no problem really. I also thought the final boss in Prototype 2 was easy and also freakin ridiculous. I hated what happened in the ending of Protoype 2 >.>
