Very creative concept and interpertation of the theme!
I didn't see the upgrade tree. My strategy was to camp in the corner and hit the enemies - I ended the game with -3600 HP lol - I was never hit. I think ranged enemies might help to prevent that. I'm also not sure, but it's seem like all levels took the same time, not sure
The level screen and animation was really well done, but honestly I wish there was a way to skip it on the end.
it could be interesting to choose to lose an ability rather than hp/damage and/or keep everything but gain some sort of drawback. You said you overscope so it's understable. Lots of potential here!