Interesting combat mechanic. Visual feedback of player damage enemy and enemy damage player effects would be helpful for player in understanding what action took place.
Additionally found a game glitch where on completing the level with no hearts left (and player not dead) in next level with this condition player never took damage. Basically the player could never die in future events.
One note to take away is when making simple games is to avoid unnecessary or excessive amount of game content as this will have unknown affects on your gameplay in your case it are the spells. There are just too many of them to understand how and when to use in a turn based game especially when the game is fast paced.
Overall a basic and simple design, interesting gameplay, fitting art, and a work well done.