Really loved the music and theming!! Also the character designs, you did so much with so little (circles, pixel art and 1 bit palette - which I also loved)
It took me a moment to understand you could fly with double jump. Only then I found out how to actually damage the bosses, but then with the large arenas they became too easy to cheese...
If you push this forwards, I'd recommend looking at Kirby and Metroid boss design. I think the theme has potential!