The only usefull Shedinja is the baton passing one.
Jolly @ Focus Sash
252 SPD / 252 ATK 6 HP
Protect, Dance, protect (If against a Cresselia, I think STAB Danced X-Scisors will OHKO, but i'm not sure)
Otherwise, use Baton Pass to a Physical Sweeper (Gyarados and Garchomp are common)
(My old, unorthadoxly risky Shed)