After playing through all the games again to do a proper voting, I realized two little flaws in your game. When running on a classic Game Boy (DMG) you will have some slowdown issues, which is almost normal on DMG! :D
But you will also have some of the sprites turn completely black during the boss fight.
I'd consider taking a look at this or blocking the game for being run on a DMG.
Fantastic game, nonetheless! :)