The art style and sound effects look/sound great! I will say, the sound effects are a little loud, and I'm not sure the music exactly matches an intense boss fight. The gameplay is extremely simple and almost impossible to lose, I didn't find myself needing to heal at all if I just focused the mage and then took them out one by one. The concept of being a boss fighting a party of heroes is smart though! IF you continue this concept, polish it, do some sound levels adjustments, maybe give the boss a few over-powered abilities like some RPG boss fights do, I think you could have a really cool almost idle-game like game where you can upgrade your boss to use new strong abilities against heroes that fight you!