A hidden menu, called the EJB Menu, has been discovered in the first three Mortal Kombat arcade games. By hitting the block buttons for players 1 and 2 a specific number of times quickly, a player can access this menu.
In Mortal Kombat, the pattern is P1 (5 times), P2 (10 times), P1 (2 times), P2 (1 times), P1 (2 times), P2 (3 times), P1 (4 times), and will allow players to watch the endings, enter their initials, and access a message from Ed Boon with some names of people he wants to say hello to, as well as some arcade .
In Mortal Kombat 2, the pattern is P1 (5), P2 (10), P1 (2), P2 (8), P1 (2), and has the same menu options as Mortal Kombat.
In Mortal Kombat 3 (and Ultimate Mortal Kombat 3), the pattern is P1 (5), P2 (10), P1 (3), P2 (1), P1 (2), P2 (2), P1 (3), P2 (4). In addition to he options from the previous games’ menus, you can also activate “Hiddens” (unlock Smoke and various other secrets on accessible through the Kombat Code), play the hidden Galaga game, as well as watch a Fatality demonstration.
This code was believed to have been recently discovered, but has been known about in MK circles since October 2015.