Severely undercosted; I'd run a 4/4 vanilla for that cost. This followed up by a couple of direct damage spells is pretty much a win condition.

Whoops my bad meant to be when ~ deals damage to a player. Fixing....now Also fixed the cost.

Still pretty good; but sanely good now, I think.

Does the cost need to go any? And what would be the best creature type for this?

Um, Eldrazi maybe? Depends on the flavour of why. Is it just some huge beast that's setting fire to the countryside as it attacks; or is it some sneaky vampire that hypnotises you into letting go of your control or... you get the idea. Falavour is malleable.

Costwise seems fine to me. Pushed; but not insanely so.

Ok cool. I'll have to give a type later once I know what set it's going into.