Mawile

I've been running her with Slowbro trick room (also works as mega chicken counter, since everyone and their mothers use it) and also have suicide Gourgeist with trick room as well. Gourgeist learns explosion and trick room, so I just set the room up and boom on someone's face I need out of the match. Then switching into Mawile gives her free reign over the opponent. If they're slower than me, sucker punch. If they're faster, do whatever I want.