Thanks for the thorough review and the suggestions! There was a lot that we still wanted to do, like making a button to see the combination list while in game and making a kind of tutorial enemy like you suggested, but we ran out of time in the end. There's definitely some things we can take from your suggestions to improve for our next game jam. I think it would be really funny to make accapella background music for a future game. Maybe next year :)
As for how the sack works, it draws 4 dice every turn by default. The sack only refills once it reaches 0 dice. So if your draw count is higher than the number of dice in the sack it won't draw any extra dice. In these cases draw dice don't really have any effect. We should've explained this better in the tutorial page.
Regarding how the enemy's actions are determined. It depends on the type of enemy, but it is basically pseudo-random, yes. Initially we wanted the enemies to use dice as well but we already had too many things on our plate.
For the difficulty balance we did want the last enemy to be challenging. Initially the person that was working on the enemies had made them even stronger, but when we playtested it we quickly asked him to nerf them, because he had made them way too strong. Maybe we should have nerfed them a bit more XD
SPOILER: As for what the ending of the game looks like. It's just the map with a "victory" text on top of it:
Thanks for playing the game and the review!