Really original combat design, I love it! I don't like how you can only cast a spell while every enemy gets to act in one turn. I defeated the badger boss by simply spamming quickflame while my party members soaked hits.
One way you could tweak it is letting the player use spells until all characters have cast one for that turn. This would also incenivize the player to use a more varied spell list. As of right now, the game feels more like a puzzle than an rpg.
All considered, it looks promising and I really want to see what you're adding next