Gengar is good and Mother Gengar is nice, but now, its just so many ways around Fainting Spell, everything is hitting faster for major damage now. Ape/Ray has one of the best matchups against it, just because 100/Tank G/Bat G will ensure a KO, Nidoqueen will be gusted for a KO while the same for Claydol/Baltoy will happen in the first few turns of the game.
BlazeTran does 100 everyturn and 20 between turns. Bye Bye Gengar even with Queen.
SP decks can just play around them easy, Dialga does well since it eliminates Queen from the equation and can poison gengar while deafen locking you and power spraying. Same for Gallade spread which does the same but spreads and eliminates Queen.
Kingdra can even, it can be teched with Tank G/Bat G/Dialga G and go to work by doingg 60/20 then 40/Tank/Bat.
Speedrill can also do the same with PPs/Bucks and Tank G.
I mean really, Gengar is like how it was during Cities, its a good play, but Gigas is gone, Machamp speed died down, Dusknoir is gone, and SP is here to stay. Gengar just can't be that devastating anymore since its easy to understand now.