Mega Gengar is all about HKOS. It has high stats to get the job done, and against slower pokemon like Palossand, Gengar is very useful. If a pokemon outspeeds, it has a high kill rate and either kills or leaves gengar at low hp. If Gengar can't kill in 1 hit but can in 2 and the opponent can't 1 shot Gengar, roll the credits. But if a pokemon like greninja shows up, roll the credits. Gengar has high potential, but I think hypnosis should land more often.