6. Riku/Ansem (Kingdom Hearts)
Square EnixYou're forgiven for thinking that an RPG which brings together Disney and Final Fantasy characters would be horrific, but Kingdom Hearts's main achievement is merging them in a credible manner; the fact that it's a brilliant game just tops everything off nicely. It has some of the best gameplay of any RPG ever made and while its story is pretty sappy, it's also highly memorable and full of great characters. Our hero Sora has to overcome some considerable odds during his journey, but the battle against the possessed Riku (Sora's best friend) is probably the toughest obstacle of all. Riku (or Ansem) is amazingly fast and can pull off a series of highly damaging attacks in quick succession - being able to dodge and parry is essential here. The close quarters nature of the arena means that he's always on your case too; even escaping for a quick heal is a tough task. It's relentlessly difficult and frustrating (you'll be seeing the preceding cutscenes a lot) but once you've bested him, it's a relief like no other.