Just tried out the game and I think there are a few things that you can improve on:
1. You should add some sound effects. You probably just haven't add them yet but even a little bit of sound played when stomping on the enemy would make the experience better.
2. The speed of the character. I think the transition between "standing still" and "moving at full speed" is kinda slow, so I think you should make the speed building faster.
3. It's a common designing mistake to put spikes or pits off-screen without any indication of where the they are, which could lead to players jumping into them without knowing where they are. A very common way some gamedev would fix this issue is by putting coins / collectable object or just a sign or arrow pointing at the safe spot so players know where they are going.
So far the things i listed above are more on the negative side, but there are still things that i enjoy, such as the art style. it also gives off similar vibe as old Kirby games which gives a sense of nostalgia. Sorry for the long paragraphs but i hope you can make your games the best you can possibly make! :)
(if you have trouble reading this i can type the whole thing again in chinese lol)