I have another moveset for Silvally, still a Ghost type, but maybe it could be an improvement?
- This is a SpA set, unlike my Atk set.
Silvally @ Ghost Memory (duh)
Ability: RKS System
Nature: Modest or Timid
EVS: 252 SpA, 252 Spd, 4 Atk.
(Yes, I do have a Shiny Silvally, and this Silvallys moveset and stats helped me to inspire).
- Work up
- Shadow Ball
- Ice Beam
This moveset might be for competitive. You can start off with a Work Up, so you can raise U-Turn's, Shadow Ball's and Ice Beam's power. Then, I would go for a Shadow Ball for the STAB and good damage.
Since Work Up increases Atk aswell, your U-Turn should be stronger.
It might be a bit weird having a setup move and a switch out move, but U-Turn can help getting out of sticky situations. Don't blame me if you waste a turn switching with no damage. :/