Really awesome game! The visuals were super polished and the controls felt really nice. I have a few suggestions but they're pretty nitpicky:
Some of the time the boss would spawn directly on top of me, maybe I'm just super unlucky but this was pretty sad because it ended a lot of my runs. Maybe make him not do damage/attack until some period after he fully materializes?
Maybe make a neutral dash input go in the direction the player is facing (this is really subjective).
Super fun game and I can't believe you made this in such a short time!!!