Wrath of the Lich King.

[Bunny]

Kael and Vashj are two of the worst encounters in the game. Illidan is the worst though. Archimonde is pretty fun except if you are a decursing class, because that's all you freaking do aside from not stepping in the fire. I think the best encounter I've done so far is Kalecgos.

Ahune was pretty fun. Horrible with most of the groups I managed to get though. Never had a chance to finish him on Heroic, nobody knew how to do him for some stupid reason.