I won't pretend I'm some analytical genius, but I've tried this set and used it to decent success, though it requires quite a bit of team support:
Necturna @ Leftovers
EVs: 252 HP / 252 Atk / 4 Spe
Ghost/Fighting give 100% perfect coverage. Focus Punch hurts Heatran and Tyranitar really badly, and it's not too hard to get a Sub up against them if you come in on a teammate that Necturna forces out. Shadow Sneak is for anything that doesn't die to Focus Punch, and of course it gets STAB. Pain Split keeps her healthy. Works marvelously if you've got a ton of hazards up. Interestingly it doesn't use a Sketch move.
In a perfect world, I would have a Flareon that would roast my coffee beans every morning, and a Vaporeon that would provide the hot water.