252 Atk Tough Claws Metagross Hammer Arm vs. 252 HP / 252+ Def Skarmory: 90-106 (26.9 - 31.7%) -- 36.7% chance to 4HKO after Leftovers recovery
Skarmory is not really threatened by Hammer Arm, to be honest. I had to edit the calculator as mega metagross wouldn't show up, but this uses his...