Here go quite a mouthful of observations written on the fly! Not necessarily ordered enough, but I think it makes sense.

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Things I like:

• I like the concept, I think you really made an effort not just throwing in some randomness, but really connected the concept of a die with Action-RPG combat (value ↔ bonus/penalty, hit points, defence). By the way, the mix of colour and number reminds me of the Uno card game. ;)
• I also enjoy the (simple) map; I had already thought before that maps tend to solidify the existence of the game’s universe in the player’s mind. Although there is no landscape (in the style of Ghosts ’n Goblins), here, but if you ever update the game, this would be one of my (minor) suggestions. :)
• And the characters are cute. Both the die head and the enemies.
  Spoilers: the swelling of the ‘slime’ makes me think of the bosses from Yoshi’s Island. :) And the two-guy enemy has me thinking of a duo boss from Kirby’s Dream Land. And their side-switching that matches their current bonus is another nice detail.

Observations + suggestions:

• Oh, big explanation pictures; I tend to do that too. XD I am always frightened there may be too much information intake for the player when I use them; here, page 2 had me make wide open eyes at first sight (just from the impression). I think it’s a bit overtaxing to process all the dice combinations — although I understand the logic of the four ‘elemental’ types of dice, and it’s not necessary that complex, but it can be intimidating.
  
  The ideal to teach complex mechanics is to have a progressive tutorial, but of course, this can be hard to set up in a short game jam context; trust me, I know, that’s why I do it partly the way you do! X) But also partly through IMPLICIT tutorial levels. I think it’s a cunning game design idea to have the player learn things without going out of your way to teach him.
  
  I think this was confirmed right in the very first battle for me: I had trouble remembering how everything worked precisely. Everything, except maybe some sparse combinations, but I remembered perfectly the four types (because it is visual thanks to colour, and simple). So I think a good strategy to help the player understand what is going on would be to gradually introduce more types and combinations as he progresses through battles, or even through the turns of a battle. Or an explicit tutorial battle would have helped.
  
  Right after defeating the slime, I launched a second instance of the game to read the second page of the tutorial once more. Actually, this gives me another idea: you could have also simply let an in-game button allow the player to access the combination list at any point! Because my way of playing and reading amounted to this.
  
  I also think that a BIG in-game help would be to have something (such as text) signal explicitly what the dice roll has just produced. (Things like "Debuf!", "Defense+!", and so on.) I know there are numbered indicators, but it is still a bit hard for me to get the action. Eventually, it sinked in partially.
• In page 3, did you mean ‘draw’ by ‘throw’? In regard to page 2.
• I think some music would also add to the ambiance — although I do not blame you, since you decided to produce the audio by yourselves. It is easy to find free suitable music for your game (I know, my good friend Kevin MacLeod provided the soundtrack for mine ;))), but maybe you wanted to keep it more personal, which is great too.
  By the way, props to you for the mouth-made sound, the ‘chiiiing’ had me heartily laughing (and I mean that in a good way). XD For the record, I did the same quite recently for aquatic bubbles in a previous game (for Mini Jam 109). I was then considering making ‘mouth music’, so maybe you could have done it (especially since there is four of you XD), in a Smooth-McGroovesque style of a cappella. ;)
• (some things I might have missed) One thing I am not sure I understood correctly: how the enemy’s action determined? Do they also throw (invisible) dice? We apparently do not get to see that, but I think it would be great to show what dice they throw, if that is the case. But maybe they don’t, seeing how the final duo operates with regularity.
  
  I am not sure I saw the multiplicator die from page 3 in the game, but that may elude me.
  
  I am also not sure I understood correctly when the sack is being drawn from, because it can happen when it is neither empty nor when I threw a (yellow) ‘draw’ die. I only understood very close to the end that you can also throw single dice… XD I thought you could only throw combinations.
• Also, on difficulty balance: while I managed to beat the two first enemies barely knowing the combinations/rules, the last one is much more delicate, especially its final phase!! Died twice within an inch of winning!! :o Maybe enable some cheats to get to the end? (I applied this trick in my game, letting the player skip a level entirely if he wants to.)
  It occurs to me I may have had invisible super dice, but could not… So the game may be more beatable than it seemed to me. Anyway, I wonder whether the last phase is buggy or not, because it seemed that the bonuses and penalties I cast were occaionally immediately thrown away, contrary to what happened during the first phase!

I am sympathetic to the game, its concept and its style, but I just spot that it may be lacking in the educational side. Enhance this, and the game will really gain something in my opinion. It is surely easier to remember all the rules when playing for some time, but as a ‘game jam minigame’, this is somewhat tough.

(My comment is meant as a constructive one, once again, I like the game and will even give it good marks! :) The concept is great.)

By the way, thanks for warning about the bug and how to deflect it, as I would have been stuck midway through the last battle otherwise!

Alas, trying once more, I stumble upon a blocking bug: I have exactly zero dice, and apparently none invisible, which means I would have to restart the game again!! ._. I am interested in knowing what happens at the end, so if you could tell me… Rarely have had luck at games of chance; this dice theme rolls against me! XD

(Spoiler, sorry)