My favorite pokemon to use when I am in the trolling mood is this little thing:
Whimsicott @ Leftovers
252 HP / 252 Def / 4 SpD
Bold (+Def, -Atk)
-Stun Spore / Memento
Bring it in on something, use Encore on a set-up move or a weak-enough attack, get behind a sub, then have the time of your life. Whimsicott is one mean subseeder. Priority on all four of these moves is simply divine. It is surprisingly beefy with maximum investment in the Defense stat, letting it take on most purely physical threats like a champ (though it does not like facing Extremekiller too much). Not only can this thing subseed, Whimsicott is great at helping to stop a potentially disastrous sweep from Mewtwo, Darkrai, or whatever. Either slow your opponents to a crawl with Stun Spore or cripple a pokemon with Memento in a pinch.
There can only be one Cat Mario.