This is ADORABLE. And I hated how many times I had to listen to *checks notes* Mousebert die. Congrats on finishing your game!
The core idea is really simple. Not including a jump button and just making it a simple left/right was a great choice. Beautiful sprites, and mix of 2d pixel and 3d background gave the game a clean and whimsical vibe. Nicely done.
For me, the game was super difficult because of the controls. J/K/L is super unintuitive, as it doesn't follow the standard WASD, and has no clear link between size other than hoping the player associates the order from left to right. I had a really difficult time keeping that straight and didn't often make it more than 10 moves before hitting the wrong key. And the pressure to keep moving and go quickly just isn't my style. I can't think of a better solution off the top of my head, either though. Maybe ASD for the sizes and mouse click left/right to jump? Or Q/E to increase/decrease size, make the transformation super snappy, and difficulty can ramp from single step transformation jumps to more frequent double step transformation?
This is still a super cool project. Keep making games! Especially cute ones with puns and mouse wizards <3