Hmm, haven't had much time to post attacks. Darn, I was hoping I would get to do this earlier. Begin by creating a smallish decoy doll with Substitute. Continue by summing up the rain and then get ready to buzz to your heart's content! Gengar may try to get ranged from us, but doing so he's just coming closer to the Thunder we'll unleash from the skies! If you need to, move a slight bit away from the decoy doll so the rings of Hypnosis don't hit you. If somehow they do seem to be coming to you, close your eyes. You really shouldn't need to, but just incase. In that case, use Rain Prayer to finish.

Substitute [smallish], Rain Prayer / close eyes, Thunder / Rain Prayer