Hi, and thank you! The idea was (but thanks to stuff in the background it didn't happen) that you get combos for kills in a timebubble and as you rank those up the music gets heavier. Will work this part in the near future. (In combo? More XP, hp regen, maybe specials?)

Thanks for playing! :)

Essentially you get XP when you kill an enemy; around wave 6-7 your character should probably be about level 6-7 (although the number of enemies spawned during a batch of a wave and the XP reward for a killing an enemy are both randomized slightly). You get one upgrade point when leveling up. The "Upgrades" button only shows up at the end of a wave if you have upgrade points to spend.

Thanks for taking the time, Edwin! You are right about the not-so-responsive rage system (it indeed waits for the end of the current loop intentionally), we originally wanted to start a drum fill when a player activates rage (a different one depending on how many bars are remaining until the end of the current "normal music" loop) and enable rage during the fill as well, but we didn't have time to implement it. We'll probably do an update though. We kinda lost track of time implementing the skill system so indeed the track switching between normal/rage is the only adaptive music mechanic in the game. Anyway, we've learnt a lot and will definitely update the game after the jam as well :)