Well a CB bullet punch still wrecks Gengar. But taking aside the details and priorities and stuff, Gengar is basically the new go to special attacker. Shadow Ball, and Focus Blast now has even better coverage, hitting the Steel/Psychics it couldn't before, like Jirachi and Bronzong. The only checks right now are Normal Special walls, such as the blobs, which both result in stalemates, Specially Defensive Meloetta, Specially Defensive Togekiss etc. Umbreon could be a viable check as well. I'm thinking Muk will get more usage as a check to fairies in general, and also checks Gengar quite well.