Unlike console and PC games, arcade cabinets aren't typically available for anyone to poke around in. This can lead to secrets going unnoticed in arcade games for years, even in the most popular machines. In October, the patrons of The Cutting Room Floor, a website dedicated to cataloging the unused and unusual parts in video games, discovered a secret menu available in the first three Mortal Kombat titles.
The "EJB menus," with the EJB referencing Mortal Kombat co-creator Ed J. Boon, have quite a few interesting options available. Many of them are diagnostic tests and internal management, but you can also set the machine to play in "free mode," modify the high score board, view character endings, play a hidden shoot-'em-up reminiscent of Galaga, and see a few secret thank-you messages from Ed Boon himself.
It's crazy to think such a popular series of arcade cabinets could hold their secrets so long. If you have access to a cabinet, and you'd like to check out the EJB menu, the video above explains the complex button sequence needed to unlock it.