When asked about Ronald McDonald's absence in Grimace's Birthday, artist and designer Tom Lockwood responded:

The telephone line level of Grimace's Birthday was supposed to have energy running through the cables as a hazard, but this was objected to by McDonald's and replaced with a squirrel Grimace could bounce off of.

While Grimace's Birthday seems to be a web-browser game mimicking the "retro" graphics of the Game Boy Color, it is actually a real Game Boy Color ROM being run in an emulator, and it's possible to extract the ROM and play it on a Game Boy Color or hardware that is compatible with its cartridges. Because the game was designed specifically for the system, its data includes an error screen typical of those found on other Game Boy Color titles that are incompatible with the original Game Boy. However, because Grimace's Birthday is intended to be played on McDonald's official website (which does not allow the player to switch between Game Boy and Game Boy Color mode), this screen is not viewable.