I'm gonna quote you here: Very ambitious idea! Took a bit for me to get what was going on, and that's not a bad thing. Seeing the first creature get synthesized gave me a nice 'a-ha' moment. The music and graphics were a highlight for me, great job nailing the aesthetic. Chiptune is satisfying.
I enjoyed the platformer aspect, I think it could have been expanded by adding fail states such as dying to the spikes or blob. I also wonder if the screen space could pose challenges for expanding on the interesting concepts you established.
There were some funky graphical glitches, nothing deal breaking. Starting the game again really breaks everything though. Funny enough, it fixed the worm which I didn't realize was supposed to be crawling (and not spinning in place)!
It left me wanting more, and the authenticity of these GBA games is really impressive. Especially since, as you noted this was your first time developing in C. Overall great execution within the limited time frame.