He doesn't really mean any harm by it, but it is a little mean. Some ghosts like him like to play around with illusions, though, so I suppose it could be worse.

[Speaking of which, here comes Gengar out of Morty's shadow, leaping... right onto his head. The idea is probably more to entertain Aggie than anything else, even if Morty's stumbling around now. Mostly because Gengar's managed to push his headband down over his eyes.]