The idea is interesting. And the cute tree is the best)
Here are a couple of suggestions:
There aren't many options for each turn (but I'm not sure if I found all the mechanics:)) For me it was like: you have, e.g., 2-4 spells, and you just use all that fits in the frame every turn. So it would be cool to have more spells to make the player choose, and more health to make battles longer.
Also I didn't get the idea why do you need to click on spells after confirming the grid.. Does the order of spells matter? If it doesn't, probably it would be nice to have some dependencies to have even more options to choose from.
I think it's really promising! Would like to see the updates)