What an interesting concept for the game jam! Just some suggestions for improvement:
- It would be good if there are some special cards. Exp: Poison (poison enemy and deals x damage to the enemy), Burning (same as poison), or some skill cards like turn speed x2 so your unit will perform the action twice before the enemy perform once etc.
- Unlock different cards after each battle. After defeating an enemy, allow player to choose maybe 1 out of 3 cards and they can use it for the rest of the battle etc. This introduce progression and the more you progress, the stronger you are and maybe you can combine different moves to make combo etc.
Overall, its a very nice game with amazing idea and you did a very great job!