Heres a reason why homebrewers and hackers are actually good for old commercial games, heres a release of the old black and white Mario Land 2 on the Gameboy boosted with colours and the slowdowns are gone, amazing work, heres the release info:

Merry Christmas!
This hack turns Super Mario Land 2, one of the best GameBoy platformers, into a fully colorized GameBoy Color game. Luigi has also been included as a playable character with his own physics.
Itís been completely done in ASM so it works on real hardware. Additionally, this hack uses GBCís extra CPU, so all the slowdowns found in the original game are gone.

release link