the fact that there's no sound is a bummer and even a few SFX from SFXR can make a diference
tip for walk animations, you can get away with a few frames
Super mario bros 2 does this and so does my game
also the text is blurry (beause godot defaut font) and a random free font from https://www.dafont.com/ goes a long way
and you could have made the power ups not dependant on a single key (also see how limited balan wonderworld is)
also i kinda feel like i should'of been able to teleport upwards