Mortal Kombat (Game Boy)
This game has a prerelease article
Mortal Kombat, now in laggy, miniaturized, four-color form. Hooray?
The GameShark code 010085D6/010086D6 changes 1P/2P to Johnny Cage, a character not implemented in this port. Nothing of him, except his name, is present in the game's resources, as none of his graphics are present (only uses Sonya's sprites just by accident).
He doesn't have his shadow kick, split punch, or a Fatality, but he does have a fireball projectile that is identical to Shang Tsung's in the game.
There are about 300 bytes of code at the beginning of the ROM (up to $000400, where the actual game data starts) that are a code/data leftovers from some kind of developer's boot monitor. It was used at the RAM-based cartridges (it does write system reset vectors manually) and intended to establish connection with some host machine vial link cable and execute remote commands. Portions of code are disabled, also there were a font someday now filled with garbage bytes ($0003C6-$0003FF). The only visible evidence of it is a routine to display the system messages on boot which contains two strings currently unused: at $000328 is
shown when boot start and at $00033E is
RAMTEST FAILED !
right after boot message in case of one of the variables is non zero. This variable $DFC4 never written even with the debug leftovers code anyway.
The game contains a secret unlockable mode where you may play as Goro himself. In this mode all character names are changed to reference members of the development team at Probe Software, along with some other minor, silly text alterations. Despite "CAGE" (Jhonny Cage) not being used in the final game, his name was still changed to "JEAN". Two string libraries containing all names and other used words for both modes are stored at $001A31 and $001AB2 respectively in ROM.