That was really fun to play! It was quite easy and I appreciate that for a game jam but I think if continued the difficulty should be upped by a bit. Apart from the beginning being a bit too slow, I love how intense the fight becomes with all of the attacks being combined and you having to frantically evade everything.
I also really liked the way you did the combat for the player, seeing all the dices bounce around each other before stopping, then seeing them multiple and so on was really satisfying and kept me wanting to unlock more abilities. You did however become quite strong in the end and I was able to pretty much take out over 60% of the bosses health in one go, it made be feel really strong but yea maybe a bit too OP. I'm going to replay this just to try new abilities and see how much more dices I could get.
The music was tense too and it was a cool touch to make it faster and more frantic as the stages went on. The visuals are simple but work really well for this type of game due to the amount of stuff going on and the border being the health bar was cool too.
Overall it's probably one of my favourite games so far, embarrassingly I never played Undertale but I might if the combat is similar like people are saying.