Cripes. Ok. Mr Mime, first off, use a CAREFUL Fire Punch or Ice Punch to ignite your hand and remove/freeze/burn that seed off of you in the best way you think is best. It hasn't got much of a hold yet, so get it good! Don't hit yourself, just use the elemental energy to kill the plant thing.

Then, I want you to use a Teleport, Fire Punch Combo from behind to set the back of that creature's hair/mane on fire. It looks flammable. And this way we'll avoid it's bullet seeds and faint attacks!