Problem is, Slaking only has Brick Break or Focus Punch. The latter of which is unreliable and the former is weak (weaker than Ampharos Focus Punch -_-). Close Combat would be great, hopefully that'll be Gen V's gift to him (well, a gift would be a new ability altogether).Here's a thought, what do you actually plan on killing with a non-STAB, non-Choice Band Pusuit? Physical Ghosts and Psychics could work but without an SE hit or an extremely weakened Pokemon, it's not going to kill anything. Also, we don't even know if Mummy always activates or if it has a chance to do it like Static.
Edit: @Blasphemy: You could just run a Fighting move to take out Heatran (Slaking has insane Atk) and hit Skarmory neutrally.
Lefties with 4 coverage moves is probably better anyways.