This is such a phenomenal platformer. Easily the best one I've seen so far this jam. Everything works incredibly well. The level design is great, the moveset is fun and unique with quite a bit of depth to it, the music fit in excellently (I think it was even dynamic! Dynamic music in a game jam, I love it!) and even the story was good. The jumping felt maybe a little bit floaty, but I quickly got used to it. The art could definitely be improved for a full release of this game, but the super-simple style you have right now actually works oddly well.
The control scheme was a bit hard to get used to, and while intuitive to understand the basics, it was not intuitive to use. It took me a long time to understand what the brother character was actually telling me to do. I was eventually able to learn the ultimate power (lol, love the menger sponge and sierpinski triangle), so it wasn't bad enough to prevent me from doing anything, but it was bad enough that when I failed it often felt like it was because I was fighting the controls more than anything else. I'd be curious to see how the game would play if you used the mouse scroll wheel to change sizes rather than W and S.
The snakes felt kind of jank. I wasn't sure how they were supposed to work, but sometimes they'd track me, sometimes they wouldn't, and when they weren't tracking me they didn't seem to have a set home point. I couldn't figure them out, and when I got past rooms they were in it often felt more like luck than anything else.
Also when I first started playing I encountered the strangest bug, which I suspect might be a Godot thing rather than your own code: when I was playing the game on my second monitor, everything worked fine, but when it was on my main monitor, my jump was so small that I couldn't even jump up two tiles to get out of the starting area with Pentagon Dad. This was an issue with both the Linux version and the Windows version run through WINE. No idea what was up with that.
Criticisms aside, I loved this game so much. Absolutely wonderful shit. Definitely one of my favorite games so far this jam. It is such a massive shame that I encountered this game on the 'Submissions with the least ratings' page. It deserves so much more.