There are a lot of good opportunities that I can see you've taken here. As a previous comment said, defending the boss instead of killing him is a very new idea that I don't think I've seen in a game before. It reminds me a lot of the Undyne fight from undertale, except way harder. If you had more time, I would've playtested the game a bit more and balanced it out, but other than that, it's very simple, clean, and well made.