Ok well this is all over the place. You said you wanted feedback on how to improve so I'll break it down honestly as long as you're willing to be receptive to it.
First of all despite giving off vibes of the forsaken WiiU game Meme Run, I can tell that there was an odd amount of effort into this, which is commendable and is the only reason I'm bothering to be comprehensive on it.
First of all it's always good to credit all the sources of art, music, and sound you use. It's a good habit to have for good developers.
ART: The art is completely random and lacks any cohesion. Using art assets is fine, and it might benefit you more in the future to either find ONE fully featured art pack you want to use or find art packs with similar artstyles that can be used together.
SOUND: The mixing on the sounds are all over the place and the coin sound especially if quite grating on the ear. The game over screen music also sounds like it has Modified Gain to make it more loud and annoying.
Gameplay: Platforming feel is something that having people test your game can help you with. I think these are the default values for the Platformer behavior and it doesn't feel great to control, especially the jumping. The gravity and fall speed it much to high for the lack of control you have in the air.
The boss fight is pretty cool, I can tell you put a lot of effort into it.
The story intro is good too, but again, the random art from random places becomes pretty distracting.
I can tell you have the drive to make stuff that is good and I believe if you keep at it, you can make great things in the future! Cheers!