I think you've got a great start here. I'm glad others mentioned below that you can run, as otherwise I'd be stuck still, too. The platforming/levels could use a little more tweaking. There was one jump where I needed to run and it took several attempts to actually land where I was wishing for a bit of good ol' coyote time or a shorter distance. Thanks for making and sharing your game!

I got stuck as well but saw the comment you made about shift to run. Made it to the boss and almost beat him I think lol
It's a fun little platformer game, with fun graphics and solid music and sound. Good job! I do think you have a (big) memory leak somewhere or you're doing a lot of unnecessary calculations. My frame rate got progressively worse as I went and was basically a crawl by the time I was fighting the boss (whole game in slow motion). After I died, the frame rate went back to normal.