I know a perfect moveset for those who do not wish to use Mega-Banette, or already have a Mega.
Banette @ Focus Sash
Ability: Frisk
EVs: 252 Atk (other EVs could go wherever you think most necessary, but NOT in speed, or Special Attack)
Adamant Nature
- Thunder Wave
- Confuse Ray
- Attract
- Shadow Claw / Phantom Force / Shadow Sneak
Allow me to explain: You endure your opponent's first hit with the Focus Sash, and also use Thunder Wave. Thunder Wave will provide automatic priority, so you can use Confuse Ray, and if they're opposite gender to you, Attract. Then you finish off with your Ghost type move.
However, NEVER use this moveset against an Electric or Normal type Pokemon, or against Heliolisk basically. If you want to use Mega Banette, replace one of the Status moves with Protect or Substitute. I hope this helped. :) (Sorry if you get stuck battling Heliolisk of the same gender.)