It was a fun experience! :) I liked the combat and the fluid movement and the layout felt good. I think you have the bones of an amazing game and it could really shape up with the addition of some new creatures that have ranged attacks, maybe ghosts that go through buildings, and then some additional functionality with the cauldron.
Some feedback I would give would be to show a score pop up when you interact with the cauldron to really cement in what was happening. I was trying to see if anything was happening to my spells or hell and then noticed it was just score (unless I missed something).
Some minor bugs I did notice were the fireballs collided with each other so it felt a tad bit clunk and if there were still monsters left at the end, and you killed them, it would do another timer and effectively skip levels. I made it to level 25 but I think I was only technically on level 15 or 16. There was a bit of pathfinding problems with the enemies as well and they would get stuck a lot.
Overall it was cool and I ended with this score.