I had a lot of fun with this! Currently, many of the battles are very slow. I think there are things you could add to increase the intensity!
For example, maybe a +1 damage for back-attacks? Assassins would be really scary, and positioning could be more dramatic!
I think the Assassins jumping back and forth can get a little annoying, maybe work on the cooldown? Or introducing some interrupt + CC cards could really add some counterplay!
The Demon Eyes are very very tanky, but also don't pose any threat. I ended up ignoring them and having them run away. Maybe consider some design changes that don't let you just ignore them. For example, maybe if their block gets to a certain point, they unleash a single powerful attack that consumes their armor? This would ALSO give the player a window to actually deal with them, without feeling like im wasting all my time and dps into their huge Armor pool.
I enjoyed all three characters, and liked how they worked together. Never used the Freeze card, I think its a little too expensive.
Lastly, I think some helpful UI elements could really clear things up. Maybe hi-lighting whichever character is next in the order Queue. Could really help avoid frustrating moments.
Sorry for the suggestion dump! I would love to see more!