Very beautiful game, great 'mood'! The music and art all fit the theme very well, and the animations were cute.
I found the controls a bit unresponsive, IMO 'on button down' is better for twitch things like jumping.
I didn't really get what the collectables did - did they increase damage?
It felt a little bit cruel to restart from the beginning when I got hit by the fifth boss. I appreciate it when jam games give frequent save points!
I ran backward and was able to fall off the level and had no way to restart without refreshing the page.