Really amazing game! I loved the art and the concept, I went for a similar "less health = more damage" idea but you did it was better with the hurt yourself mechanic and power switching between your attacks.
If you wanted to improve, I suggest some form of cooldown (maybe related to attack power). I was literally able to fly across levels with the sword attack. I was also able to stand in an area, attack nothing to build up a ton of power on the lightening (my favorite attack). I suggest changing the power swap to be based off of landed hits rather then attacks.
Overall an amazing game!