Hardest fights?
For me, the hardest battles in the game would have to be the living statues fight in Extreme Cosplay, which has a terrible setup and restrictive fighting area, and the fight against Dettlaff at the end. Fck him and his stupid bats, goddamn.
Also, while they weren't especially difficult as such, the Caretaker fight in HoS and the fight against the Wicked Witch in BaW took ages for me.