Would Trick Room work with your team? Musharna is pretty limited movepool wise, but it can setup Trick Room decently because of its bulk. Once Dream World is out, its Telepathy ability will help it a bit in doubles battles. Trick Room / Yawn / Psychic / Light Screen (or Reflect). You could add another attack for coverage. Shadow Ball covers other Psychic Pokemon, but still leaves you open to Dark types. Energy Ball might seem like it gives you some decent coverage, hitting Tyranitar and Jellicent, but it'll hardly dent them.
Musharna is a pretty cool looking Pokemon, and I hope it receives a load of new moves with tutors in the upcoming 3rd title/3rd generation remakes.