Here's the few details I'd recommend improving:
- I don't see a reason why wouldn't the main character be able to attack upwards and downwards.
- If you already used so many sounds from Deltarune, why not use the music as well? Or any other music, just not silence.
- The only useful spell in my opinion is the healing. Invincibility is way too short to be useful and supercharge only works once it seems. I think it would be better if instead the invincibility spell lasted indefinitely but for 1 attack only and supercharge lasted for a few seconds allowing to get multiple charged hits per charge.
- A pause menu would be great.