Really nice platformer, I enjoyed playing it. The art is pretty cute.
Some thoughts:
1) I think the spikes should have a more contrasting color.
2) Even though the game is not that hard, I think you should have two hits per live instead of one.
3) I would love to see some animations! (like for the start of the boss battle, I think that could be cool but still small).
Congrats, great game!