The arcade versions of Mortal Kombat 1, 2, 3 and Ultimate Mortal Kombat 3 each contain secret menus that only recently were uncovered.
Late 2015 the secret menus, named the EJB menus after Mortal Kombat co-creator Ed Boon, were documented on The Cutting Room Floor, a website dedicated to uncovering cut content from video games. This week, YouTuber YourMKArcadeSource tested the menus out and documented them in the video, below. He explained the process on TestYourMight.com.
Unlocking the menus requires the execution of an extremely tight input command - fitting, perhaps, for the fighting game series. It involves pressing the correct block button a certain number of times. For example, to unlock the menu in Mortal Kombat 1, you need to do the following:
P1 (x5), P2 (x10), P1 (x2), P2 (x1), P1 (x2), P2 (x3), P1 (x4)
So what does the EJB menu contain? In the original Mortal Kombat arcade, released on 8th October 1992, you can perform diagnostic tests, select coin bookkeeping, and trigger a game audit for things like chip failure, frame errors and system lockups (there's also mention of a Green Ninja Counter - possibly a reference to Mortal Kombat's hidden Reptile fight).
There's also "Hello", which displays a screen of shout-outs for 10 seconds. You can also enter your initials on the high score screen.
And finally, you can trigger a new sub-menu that displays the selected character's ending with the game credits.
The EJB menu for Mortal Kombat 3 lets you unlock the Galaga mini-game as well as playable character Smoke. The EJB menu for Ultimate Mortal Kombat 3 lets you play the long "Supreme Demonstration" of Fatalities, Animalities, Babalities, and Friendshipalities.
Can you imagine if these menus were known about when Mortal Kombat was popular in the arcades? It would have been coin-op chaos, I can tell you.