Fun game! I was impressed by the variety of enemies, especially with multiple bosses! It was also nice to several powerups to try out. I also liked some of the features like displaying enemy HP and having ladders. The enemy death animation/effects were really nice too. In general the graphics were very cute, I liked the style.
I missed not having a variable height jump & would've liked to see that. It is a design choice so it is reasonable to choose not to make that feature available, but I would've enjoyed the game more & it would've made combat feel more skill-based. I also expected to be able to jump or glide after falling off a ledge, but those abilities are only usable after a normal jump. Again, if you don't want to add that feature it's your choice, not really a game flaw, but I would've liked that feature & I am used to it from other games.
The sound effects were much louder than the music, so I would've liked to see that fixed. In a fully featured game, seperate volume controls for BGM and SFX would be ideal, but making the volume of BGM and SFX closer would be good even if you don't make volume controls. I would also have liked more feedback when the player is hit. It was hard to notice sometimes, so a sound effect or a visual effect in the center of the screen or near the life bar would have been good. Some people like screen shake but I recommend against using screen shake unless you make it optional. Some people (including me) can't play games with too much screen shake. It would be a good choice if you make it optional, though.
All in all, it was very fun to play & there were no major negatives. Nice work!