Awesome game !
Firstly, the artstyle is amazing, great job :) Only visual thing i would suggest its that the selected part reamins white, so you can clearly see what you selected. And now, about gameplay, i think as we know the number of life we have, we could know every number (the cost of life of every card, life recieved whith clock, damage done with fireball, and damage increased by sword). I think sword doesnt work (i always do 30 damage), probably thats why it was so hard to reach wizard, and imposible to beat. For the cards you can add more visual info (the one i previously said) in the gameplay, or a simple sprite explaining the 4 of them as a tutorial before starting a run and you can always watch it with some key as Tab to remeber it. You should also explain better the turns system, i firstly thought you could use cards or attck in each turn but not both, just say in each turn you can use up to 2 cards and to finish the turn jhust attack. In conclussion, solve the sword card that seems not working and give more info to the player so its more user-friendly, cause the gameplay, as it is know, its awesome. This game has a lot of potential, i will absolutely return here to see if you polished it and replay it.
Also, you can try my game if you want, it just takes 5 minutes ;)