Grimace's 52nd birthday was yesterday, apparently, and it is celebrated with a few things, but of most interest to us here, one of those things is a retro-style video game. It's an actual Game Boy Color ROM (made in GB Studio in seven weeks by Krool Toys). And it is playable in emulators and flash carts!
(https://ia802604.us.archive.org/22/items/grimaces-birthday/grimace%20birthday%201.jpeg) (https://grimacesbirthday.com/)
"Grimace's Birthday" is playable in your browser at:
https://grimacesbirthday.com/
This homebrew game is available as a ROM here (though you should rename the ".gb" extension to ".gbc"):
https://archive.org/details/grimaces-birthday