Fun game! I love the art, and the visual indicator on the character sprite for showing how much XP player has in current level is clever and works well. As for feedback, I think the game could do with being a bit harder. At some point I could just stand still and everything would die before touching me most of the time. I also found that
waves start of hard and then get easier. E.g at wave 4, the new monster for that wave, the one with a bunch of eyes, only comes at beginning of wave. Then there's only the easier monsters left, so it's like each level has a descending difficulty curve while the player gains power, resulting in trivial difficulty. Another thing is that the rotating balls and the aura spells look very similar in the upgrade screen, so I ended up choosing the wrong one a bunch of times.
I also love that the AI dominating the world is a .tscn file
All in all very nice work!!