I liked the experimentation to find new spells! Switching to the right spell felt overly difficult, I often had to pause mid-fight to switch out to a new spell. It felt like there was just not enough space for the spells I wanted to use. Some of the spells felt pretty useless, though it was cool not realizing what bonfire did until the room went dark! It would also be useful to be able to switch between selected spells with hotkeys, maybe a 1-9 hotbar of spells would work better?
In terms of pacing, it was a bit overwhelming to get two turrets + boss + infinitely spawning enemies + a dark room all at once. I think it would teach the player better if some of these were spaced out more, like a single room that is dark to teach the player the usefulness of bonfires, before putting it all together.
Discovering different ingredients was cool, though the third option only had 1 choice. There were a bunch of spells and it was fun to experiment with them. Perhaps 2 options each, 2*2*2 = 8 spells, would have been more approachable?
On a technical note, it looks like the projectiles and attacks all had full collision which meant the player would often get trapped between four enemies or get knocked around by bullets, which felt a little unnatural. I went from 100% to 0% health and punted into a wall because of this, where I figured out that the player did not die.
I didn't use Dash at all, and didn't really get the purpose of some of the spells (the wall-creating one mainly).
Well done for a solo project! I hope you learned lots of things.