Found a set that might boost Mega Gengar up lil' bit on the ranking, where it's basically The Switch Forcer Of Satan. Or if you're facing someone who doesn't think to switch the Frustrating Trapper Of Satan. So basically Perish Song Gengar but hackmon'd.
( ͡~ ͜ʖ ͡°) (Gengar-Mega) (F) @ Focus...