This was nice! Though A few comments on the visuals:
- The reference resolutions for the assets weren't designed consistently. The slime sprites don't match the pixel size of the other sprites. It's a very important aspect of designing pixel art for games to match the pixel ratios of every asset. Though the slimes themselves looked pretty!
- The spikes would blend into the background sometimes. This made it hard to properly navigate through a level on the first try. An outline on the spikes would have helped with this immensely.
- Although it may have been a stylistic choice, try and avoid jaggies and stray pixels in the art! This can be seen everywhere on the background assets,
I did enjoy the music though! As well as the color palette you used for this, nice and vibrant :D Movement took some getting used to, but it's on the right track! Good work.