Stellar game! It felt very authentically Game Boy, the environments were all very cool and felt distinct, and the music is awesome. I unfortunately got filtered after getting the parachute, I couldn't progress where (I assumed) I had to go (left of the mid-point of the tree) but maybe I missed another section I needed it for. But still I enjoyed the game a lot!
EDIT: I did want to mention I experienced a lot of lag at the first boss, and I think maybe the damageable walls had something to do with it because I encountered a bit of lag later on in the shroom section where there are also some damageable walls. Not a game breaker but it did make the first boss a bit easy.