Its pretty fun! i really like the idea and theme implementation, and the way it was here was pretty cool! if i had to give feedback though, i guess it would be giving the player more agency, though i understand that this would take alot of time to implement which may not be feasible in a jam timespan, i think it would be cool if you are planning on a continuation of this game
an idea is maybe that alongside picking the upgrade you also pick the dice you will be fighting againts, and instead of having every dice roll 1-20 it could have enemy dice that rolls 10-15 or 3-16, you can also connect picking the dice you will fight alongside the upgrade system so it would make a really good risk reward system, like imagine having to fight a dice that rolls a 15-17 but if you beat it gives an extremely powerful buff!,
another idea is to have more incremental growth, have your player start as a 1-6 die and can incrementally grow, this gives much more freedom for the upgrades you can make, like a simple +2 on floor or +3 on ceiling, another thing to maybe add is lives or hp, make the enemy and player dice have a number of lives, this makes each fight less rng based while still keeping the rng focus, and would make the game feel more fair and balanced, of course this would also play into the upgrade aspect, you could make more unique buffs like removing 2 lifes on win but also taking double damage,
for feedback on other aspects besides gameplay, is that i would like to see more effects and polish put into the game, a simple way to do this is just to scale up/ make the ui brighter when selected, another thing is maybe the dice when rolling shakes around a bit, have a bit of camera shake and camera zoom shake when a dice finishes rolling,
another thing is to maybe make a win/lose animation, it really doesnt have to be anything complex just tween the dice to slam into the other dice knocking it out,
i could probably mention having like custom art and fonts but thats really going into the EXTREME nitpick category which i am already crossing the boundary off
Sorry for the long comment and feedback, i promise i dont hate the game i actually think its REALLY GOOD!!!! i really think this game has potential and could make a really good rougelike if continued! i already like the concept in this short jam game !!!