HEY, what a cool concept! I am really enjoying it so far, so take what I say purely as feed back, everything is mostly related to clarity and clarity is super important in a game like this were its a entirely unique system.
Imo turns are way to fast and confusing. I would love to see a half speed mode and some more confirmation on what's even happening. being able to slow down and speed up as the player is what monster train does, lets you slow down when you are figuring out how things work, and speed up when you kind of start getting it.
Another fix to the problem above would be to just store the damage to each side, then deal it all at once after the ball stops, so that the player has time to realize how much damage is gonna be dealt.
Feels like your going for a retro-vibe, so I know mouse controls might not be what your considering. But I think for a game like this is might be somewhat necessary, tool tips and in game explanations of things would go a long way. Little pop ups to explain key words, etc. Plus moving the board around on mouse just seems like it would be more intuitive. This could go against the retro vibe as what I am kinda suggesting here is "be more like modern deck builders" which you don't have to be if it would kill the vibe.
Big side thing, took me like 5 runs to realize breaking boxs damage me. That should be made ALOT more obvious imo. Maybe a damage animation or damage number over the character would help.
Gameplay wise I feel like there was a lack of agency during the turns, most of the fun and strategy comes from building the board I found. Which makes the first fight kinda a crap shoot. Since you always have the same board. Not sure how to fix this, maybe add a free random part choice at the start of every run?
Again I am just trying to give feedback, I am honestly loving the game so far! really fantastic work.
Edit: Also Bug it un-fullscreens every reset