Very nice art! The music, the art, the gameplay, all nice and works smooth.
I haven't seen anyone talk about the collision yet though. When you get the double jump (though I'm sure you can do this sooner as well) you can hug a wall and just keep pressing space and I got outside of the world and fell infinitely doing so. It seems like your detection for being on the ground is through a collider check on the player rather than something like a raycast that's pointing down. Just wanted to bring that up!
Still this is very impressive and you should be proud!