Love the gameplay mechanics!! The art style is also very nice!! Only thing is the borders and characters do clash with the background a bit on some levels, making it hard to see what you're doing.
In terms of the sound design, the ambient sounds is perfect and the piano sounds for the movement of the boarders wasa also very nice and unique! The only thing I'd change is for jumping- I'd switch bird chirps to being a part of the ambience/background noise but less frequent, and having a more standard jumping/landing sound. little air swoosh or something like that