Fun concept with the tradeoff for each powerup, buffing enemies in a different way for every buff you give yourself.
That being said, I was struggling a bit with understanding when I got hit and when I was in range of an attack, so I wasn't sure how to position myself and time my attacks, often dying pretty quickly.
If you plan to continue the game I suggest adding visual and audio feedback for getting hit and for when you stop being invincible after a hit. Music and more different sfx would also help a lot, the sound of hitting an enemy was a bit loud against the silence of the game.
The penalty idea was nice though, with how you could strategically weigh the buffs you want VS not making the enemies too dangerous to fight against.