I like the 1-bit-ish aesthetic, and the puzzle seem like they're increasing in difficulty at an appropriate rate. Some of the level seem like a double repetition of the previous level, and I think that could be reworked a little bit for the flow of the game.
My only big pain point is the control scheme, I'm so use to using space as a jump in every game that using W seem like a chore and it mixes up all my muscle memory. If the jump was tied to Space and the expanding to a different key, I think it would make the whole experience more pleasant. I also think the teleportation should be possible when the main character is in big form, feels weird to just hit the 2 keys all the time to teleport back.
Another little poitn is that I think it would be nice if the jump heights of the characters were made so that when the main character jumps at is maximum and gets big, the secondary character can still jump on it with his double jump. I had to go back and forth between the characters multiple time to reduce the height of the main character so the other one could get on top.
But all in all, I like the pleasant music, the aesthetic is simplistic but very sweet and the difficulty curve and levels quantity is great! Keep it up!