Insanely polished, and quite fun! I managed to get to the end with a random deck that got me some good stuff to start out with.
The combo system is pretty interesting; it added a lot of pressure to make decisions quickly, and mapping all the controls onto arrows/WASD (even the menus!) was inspired, since it created a very seamless UX.
I was a bit frustrated with being able to accidentally shoot myself with a fireball, or heal an enemy. I'm not sure there's anything to gain from being able to do that (unless there are some builds I missed?) so it feels like it's just arbitrarily punishing the player. I wonder if having healing always target yourself, and maybe having attacks with up attacking a random side would be a better experience for the player?
The enemy variety was great, though they all had so little HP that it didn't really feel like I needed that big of a combo to deal with them. Perhaps I'm misremembering enemies towards the end, but either way, I never really spent any effort figuring out who is the best enemy to attack at any given moment, except when counting number of enemies per side for AOEs, or the mirror specifically. I.e. it feels like the player should be rewarded for getting a high combo, such that they're able to beat enemies they couldn't otherwise beat?
(Also, art and music was incredible.)