Very neat and fun demo, I love the animation and design of the main character, and the enemies are pretty cool too! It took me a while to figure out the controls and how to deal with enemies, but killing things simply by running into them is honestly such a brilliant idea for a minimalist game. Plus, it's an interesting twist on the usual mechanic where monsters damage you on contact, except we're quite literally the monster here! The player feels nice and snappy to control, although I think stronger gravity and a harsher jump curve could be suitable for a feral predator-style character.
The minimal environments could be effective, but I think there are too many big and empty or repetitive spaces in the map, which kinda draws attention to how simple the graphics really are. The escape segment with the jellyfish "mini-boss" was also a cool idea that fits the theme very well, although it kinda lacked a clear win condition. I think the idea is that we get high enough that we can jump on the jellyfish's head, but it's pretty easy to just barely miss the jump and die anyway.
The main music theme is cool, but it seems that all the audio in the game is positional for some reason? The music and other sounds played from the left or right speaker depending on where I was in the level. I think it might be a case of using AudioStreamPlayer2D where the generic AudioStreamPlayer would suffice. On the subject of audio, I think sound effects for the player jumping, landing, and dying would be a nice addition!
Either way, a great concept that I'd love to see fleshed out into a full game!