Thanks-I can see why you think he's quite good now thanks to priority Stun Spore. Definintely has more use than the SubSeed set.

I ran the standard defensive set, only with 252 HP/252 SpDef/4 Def (and Calm over Careful/Impish). It was Taunt/Stun Spore/U-turn/Giga Drain. I instead run Taunt/Stun Spore/Hurricane/Giga Drain Whimsicott. I might do Taunt/Encore/Hurricane/Giga Drain Whimsicott next.

I was reading through the RU stats thread and saw that you thought Whimsicott was actually good. Would you mind telling me what set it was? I'm quite interested since pretty much everyone else says that it's terrible.