Love the game, funny thing being I just played the undead set all day and came to post a comment only to find the dragon set out already.
Game's really fun already, though a few balancing issues to be had.
Spikes need to be buffed, and poison needs to be nerfed. Tried to make a spike build but I could never survive long enough to bring it to fruition. Spikes are just too inefficient since they deplete so quickly compared to how much they cost. You're better off just attacking instead of using them.
Healing also needs a rework, something like 2 uses before it's banished from play that fight but it also individually heals for more. I forget the name but there's that demon card that brings back all 0 cost cards, and I would use that to farm heals every battle. I still ended up losing to a frog girl that stacked 30 poison on me...
The beast set needs more defensive moves, something like a parry move that when used on an attacking opponent it reduces their dmg whilst dealing dmg. Pierce defense would also work nicely with the theme. A reflexive parry would also work amazingly, where for each attack you reduce the dmg and deal dmg.
Would also be nice to have prestige cards or something. Cheap/weak cards that you can bring into your next runs by removing others. Something like a 0 cost 5 dmg quickswipe attack. The starter deck is just too bloated with cards you want to remove quickly to keep the rng from filling your hand with inefficient cards.
Would also be nice if the mystery events are set to not repeat each other each map. I had a map filled with the pits and lost in them all. Ended up with 3 tentacles in my deck and lost against the boss.
You could also have achievement systems to unlock cursed auras on start that make the game harder but gives some unique bonus. Like enemies regen 1 hp per round, but you heal after each win: 10 for normal/ambush or 25 for elite. Another being you start each fight with 2 strength but also with 5 weak. Similarly 2 shield but 5 fragile. Another is you lose 1 gold each turn but gain 20% more rewards from fights.