What does Mummy even do?

When other Pokemon hit you with a physical attack their ability becomes Mummy. Other than that it's just like the ability Simple

Simple doubles the effectiveness of stat modifiers, both positive and negative. For example, if Defense Curl is used, the user's Defense stat will increase by two stages, rather than one stage. Similarly, if Tail Whip is used against this Pokémon, its Defense stat will fall two stages rather than one stage. Stat modifiers are still effectively capped at six stages. Simple also doubles the effects of critical hits to 4x regular damage as opposed to 2x.

Only Numel, Bidoof and Bibarel have it. Woobat/Swoobat have it as a dreamworld ability that you can't get yet anyway.

Instead of thinking it similar to Simple, think of it more as someone using Gastro Acid (negates abilities) on you, but now it's infectious when you're hit with a physical move.

Could be abused if you have an Archeops that attacks an allied one in a double battle, hehe.

quote ShinyShuckle

It should have been Zombie, not Mummy, though.

Mummy takes care of the house and kids while Daddy goes out and works.