I was thinking that if I were to be in a triple battle with Cofagrigus on the left, a Spiritomb in the middle and Shedinja on the right, I could use a priority move with Cofagrigus to transfer Mummy to Spiritomb, then use another priority move with Spiritomb to attack Shedinja.
That way I would end up having a Spiritomb with Wonder Guard and with it only having a weakness to Fairy. The only problem is that I heard Wonder Guard is non transferable except with Trace, but nothing specifically talks about Mummy. Since Trace is an ability, I'd imagine Mummy would work too.