Very ambitious to make a deck builder, but you pulled it off pretty well! I agree that I would have liked to have some indication of what the enemy was doing (either STS-esque telegraphing or at least knowing what moves the enemy could do). It would be great to see some animation from the enemy to see them attack (even if it was just changing the position of the same sprite).
Also a small bug: if you change the viewport size (I wanted to full screen to take in the nice artwork), the game stays in the same sized window, but the UI takes up the whole viewport.