The answer is Thunderbird. 43ForceGems got it right first.
Thunderbird flies, and since his fight is in a battle sequence, he only gets to move left and right (not counting moving up or down while he flies). I originally said "spell" instead of "power," but that would have been too easy, and you need the Thunder spell which exposes his face. The fireballs that he shoots take a good deal of health away if you get hit and he starts to move faster when you get his health low.
So, its 43ForceGems turn.