Or just use Togepi/Togetic's Extrasensory.cornymikey said:incredibly easy way to beat morty's gengar.
Get any level pidgey/pidgeotto, attach a shed shell, and spam sand attack. His gengar can only use sucker punch and shadow ball to hurt you but they will both fail. Mean Look doesn't matter with a shed shell attached. Just wait out Hypnosis. When the gengar's accuracy is to its lowest, switch to any pokemon and take him out.