Ok, I might be stupid, but doesn't it say in the very first post that EVERY SINGLE TEAM must use a Super Size Gourgeist and can only be 3 ghosts? So how on earth will some of you have a team of Gengar, Banette, Aegislash, Golurk, Spiritomb and Froslass if you can only essentially pick two and get saddled with a Gourgeist?
Its bring 6, pick 3. Gourgeist just has to be on your team. You don't have to use it every battle.
OHHHH! I'm dumb. Then I'd probably do Spiritomb, M-Gengar and Aegislash. ^_^
Wouldn't focus too much on M-Gengar too much. You'll be unlikely to run into it but 252+ SpA Shadow Ball from a Scarf Gengar OHKOs and defeats M-Gengar all day.