Fly kick is definitely busted right now.
It removes a charge of every single status effect in the game, so it completely trivializes 2 of the bosses, including the final boss. Other than that though, I really enjoyed this game. I played 2 full runs where I beat the final boss, though of course, as explained by this message, one of those runs was far easier.
SPOILERS FOR BOSS FIGHTS (DON'T READ IF YOU WANT FRESH EXPERIENCE)
I was able to fly kick the one that mutates 4 or so times and it just died on first phase, completely negating any danger I would have been in. The final boss was basically the same, except it got off a single turn of 20 damage and that was it.