Through a series of button inputs, a player has found previously undiscovered menus that lay dormant in the arcade versions of Mortal Kombat 1, 2 and 3. How did they last so long without being discovered?
The newly discovered menus were personally programmed by MK creator Ed J Boon, and display as “EJB Menu” after his initials.
The MK1 and MK2 menus allow you to watch various character endings, input initials directly into the leaderboard, run debug and diagnostic tests on the game cabinet, and do something called “coin bookkeeping.” There’s also a “Hello” option, which YourMKArcadeSource speculates is simply a list of people Ed Boon wanted to give a shoutout to. Fittingly enough, the first name on the list in MK2 is “mom.”
MK3‘s Ed Boon menu is considerably more robust, and includes an option to immediately unlock hidden characters. It also allows you to watch every fatality—a demonstration normally reserved for players who have beaten the game on Master difficulty. There is also something called the “Penacho/Miller Game,” which fires up an impossibly difficult Galaga clone.
It’s currently unclear if these hidden menus exist in other iterations of the franchise, or on any home console versions.