I made it to level 10. I think the gameplay's pretty decently intuitive, especially with the tutorial explaining things, so I had no issue figuring out how to play. Was confused on why blank dice were showing up when they do nothing, but maybe in the future you can modify the dice in some way? That is, in game, the player could collect another die or use an upgrade somehow to change faces.
Some things about balance: once you start getting a few levels in, your sword attack becomes less and less useful. With its low output damage the game kind of becomes mostly running away from enemies and hoping you get fire and lightning magic. I like the whole pick 5 mechanic, though, which helps add strategy to the randomness.
I think sword attacks should maybe be a little more powerful for the risk it takes to get close to an enemy, and also maybe the ice attack should have a slightly greater range because it doesn't feel anywhere near as useful as fire and lightning. Or to give the sword more importance, maybe there should be more low defense but high attack enemies (I think the spider might have been one, but it still had >1 HP so the sword is a dangerous tactic on it).
I would say a way to heal would be nice, but the tutorial implied that endless is not the final form of the game's campaign, so that's less important right now if it'll be structured differently anyway.
Also, even though you did explain what he speed stat meant in the tutorial, I still found it a little tricky to try and predict where I'd be safe from an enemy and where not. It was dependent on the die roll of the enemy of course, but was movement based on speed multiplied by the die?
Anyway, balance is a tricky thing to fine tune because every new thing you add could potentially break something. But I also recommend checking out Mini Dice Battle, also in the post-jam -- it has a similar idea except you control multiple characters, and coins scattered about the battlefield encourage you to move to different places.
But I do want to mention that it's nice to see you have a decent number of enemy types, and they're introduced gradually with increasing difficulty, easing you into the game.