Hmmm... Villain... It's kind of hard to remember the villains because I'm always rooting for the protagonist. LOL. But then, I would have to go with Lord Loss from Darren Shan's book entitled Lord Loss. Beating him wasn't easy, and he was really cunning to begin with. You have to play chess in five different boards against him simultaneously while your partner has to beat his right-hand man in a physical and magical duel.