I think this card is nice, it allows you to increase a creatures damage drastically, however you still pay the equivalent of a middle range creature for it and it can be easily countered by killing the creature to which it has been applied. This would cause a lot of damage on a ruby dragon, however he would only last 2 turns.
I would increase the upgraded cost to 6
but otherwise I think its ok
Im just a little bit worried on whether this would be op on a well grown lava destroyer