What a great platformer! I love your graphics and sound. The gameplay is pretty strong, too. 

Your camera is doing a lot of good work to frame upcoming challenges properly. There were a couple times where there was a blind jump, but you had frogs or skeletons jumping below to show there was a floor. I really like how you use the normally unused D-pad down to shield, finding a 3rd button on a limited controller.

My only issue was that a couple sine-wave ghosts spawned out of the ground right in front of me and were unavoidable. It feels like they were either placed too low, or that there wasn't enough time for them to be visible due to their moving left while I was moving right. If they all spawn in at the bottom of their wave, it might be worth adding a boolean to their code to be able to choose if they start at the bottom or top of the wave.

This one has the most "Gameboy-ness" of what I've played so far. Great work on sticking so closely to the original specs, I got pretty laissez faire about how my sprites follow the hardware rules. Thanks for a lovely game!

Looks good sounds good and feels good. Pretty amazing! Some enemy placement seemed off or annoying but the ohter parts are pretty good.

Played the whole way through. Graphics were spot on, really took me back to those Game Boy days. I see the ambition here. I hope i had more days to build mine. Good luck!