I was getting absolutely creamed on the first wizard before realizing that the roll results were cumulative. I had initially thought I was just rolling until I found a combination of dice that you actually wanted to spend your turn casting. After that epiphany, things made a lot more sense. I gotta say, I was completely caught off guard by that wizard getting yeeted off the tower (in the best way possible, of course).
Balance wise, it feels like there should still be some intermediary punishment for rolling skulls. Otherwise, it seems like the play is to just roll until you have only one free skull slot remaining and then fire it off. Late game, this kind of fixes itself by way of multiple skull dice. In that case, you really do have to care about whether the risk of hitting a ton of skulls all at once (and subsequently bonking) is worth some added stats on the spell.
I also liked the art, sound, and animation on the dice. I'm also a fan of Die in the Dungeon, and I think the color and sprite style really paid homage to that.
Overall a fun little game! I wouldn't have guessed it was your first jam submission.
PS: Glad you eked out a submission before the deadline! My submission was at about 8 minutes after scrambling to get all the buttons in the UI to do the right thing.