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!
"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