Very interesting and well put together card battler. I beat all 3 stages.
I feel that with a bit of tweaking, this could really shine. The game seems a bit easy, with only stage 3 having more difficulty. The cards feel a bit too random, maybe have a pool of cards that all have to be used before the pool is refreshed. After learning that the counter attack only occurs if the player’s shield or health is damaged, there is no great reason to stack shield, might as well let enemies break the shield to counter attack because the counter can be a bit too strong. Maybe the counter value should be lowered some amount each time it is used. I really like the Dice mechanic added to the dice, though I think using multiple smaller dice would make more consistancy. 1d20 is very random compared to 5d4. Each have the same max damage but the d4’s will be more consistent. That would need a lot of player testing to really tweak the values nicely.