As a Pure Ghost-type, Misdreavus is only weak against Ghost and Dark.

Because your posts are so sparse, I can't tell where in the game you are, but there's a Shadow Ball TM on Route 210. Someone on your team should be able to learn it in order to fight back. I don't understand how Misdreavus is getting multiple attacks in a row, though...that makes no sense at all. Are your pokémon getting paralyzed or infatuated or something?