Nice 2d platformer, feels good to play, I like the visuals and music. Great job for your first jam!
Some suggestions for improvement:
- some visual effect when you land on enemies and kill them and maybe the player bouncing off them in a mini-jump
- implementing damage or having to restart the level on hitting enemy or spike from the side
- the mushrooms would be more interesting if they changed some aspect of the gameplay when picked up rather than just giving points