Sega Genesis
Blood Mode: From the Code of Honor screen, press A, B, A, C, A, B, B. If this was done correctly, the text will turn yellow and you will hear Scorpion say "Get over here!"
Cheat Codes: On the screen where you can choose to start or change options, press Down, Up, Left, Left, A, Right, Down. A new menu choice, "Cheat Enabled," should appear.
Here are descriptions of each item on this menu.
PLAYER ONE: Chooses who is on the left in the scrolling side bar, the medal display, and the "Test Your Might" screen.
PLAYER TWO: Chooses who is on the right in the scrolling side bar, the medal display, and the "Test Your Might" screen.
PLAN BASE: Select from four orders in which your character will fight other characters. You can pick a set order or choose "Random" which allows the computer to choose one for you. This takes effect for the game and for the demo.
MATERIAL: Picks the material for the "Test Your Might" screen.
CHOP 1/2: Picks the number of rounds between each "Test Your Might" screen. Takes effect in one-player mode. Enter 0 to disable "Test Your Might".
DEMO: Demonstrates different parts of the game.
CAMEO: Displays background information on PLAYER ONE.
PLAN BASE: Displays background information on PLAYER ONE.
BIOGRAPHY 1/2: Displays biography screens for PLAYER ONE.
MEDAL: Shows the winning screen after you beat someone in two-player mode showing PLAYER ONE as having 20 consecutive wins vs. PLAYER TWO.
CHOP-CHOP: Brings up PLAYER ONE vs. PLAYER TWO in the "Test Your Might Screen," chopping the material selected above.
FLAG 0: Brings the right player's energy to DANGER at beginning of the round. If Reptile appears, the player has full strength for the first match. During endurance matches, the second opponent has full strength.
FLAG 1: Brings the left player's energy to DANGER at beginning of round. If Reptile appears, the player has full strength for the first match. During endurance matches, the second opponent has full strength.
FLAG 2: Guarantees shadow appearances on the Pit Stages.
FLAG 3: Changes shadows on the moon to a face or the initials "BYC". Works when the sound, music, and effects test are not all set to 1.
FLAG 4: Reptile appears with hints at the start of each stage.
FLAG 5: Infinite continues (credits never decrease).
FLAG 6: The computer will use fatalities.
FLAG 7: Locks background screen as "The Courtyard" until the fight before Goro.
BLOOD CODE: Turns blood on and off just like ABACABB.
CHEAT CODE: Turns off all cheats and clears all flags (FLAG 1, 2, etc.) If the cheat menu is exited with CHEAT CODE turned off, the Cheat Enabled choice will disappear from the menu.
FIRST BACKGROUND: Chooses which background appears first.
Fight Reptile: Enable the Cheat Menu. Now go to the cheat menu and set FIRST BACKGROUND to "The Pit," FLAG 1 to ON, and FLAG 2 to ON. When you start, you're at the pit screen, and the moon shadows will always be there (you'll see Santa Claus, the witch, etc.) To guarantee a fight with Reptile, never block, get a double flawless, and do the fatality. Good luck!
Hidden Character: There is a glitch in the game that allows you to play against another character not meant to be there. It is not like Reptile, who was programmed in. Instead, it looks similar to the old boss code for the Super Nintendo version of Street Fighter II. To get to this character, you must first put in the Blood Code and the Cheat Code, then turn on flags 0 and 2. Now, when you get to the endurance matches one of them must be in the pit. Beat the character without using block, get a double flawless victory, and perform the fatality. Reptile will once again appear. Beat him, and the hidden character will jump down.
Reptile Illusion: When you are fighting Reptile, press Start on Controller Two. When the player select screen appears, Sub-Zero and Scorpion will turn green.
Super Nintendo
Fatality Glitch: To see a cool fatality glitch, take Sub-Zero, (it's easier to do if you're not really fighting an active opponent, so leave the second player "dormant") and beat your opponent one round. On the second round, kill them until they have only a tiny bit of energy left. Now, just keep throwing your Ice Blast (Freeze move) and eventually, it will say Finish Him/Her when they are frozen. Do your fatality and the statue will crumble, but your opponent is still standing, still dizzy!
Fight Against Goro: Fight the three endurance rounds with Rayden. On the third endurance match, make the match last three rounds. Now do your death move, and you will fight a T-1000 Goro.
Fight Against Reptile: To fight Reptile, win with a double flawless victory on the pit and execute your death move. DON'T KNOCK THEM DOWN THE PIT! This cheat only works on one player mode.
Insane Mode: Set the game difficulty on Very Easy, and let the game beat you every round until you reach the Hall Of Champions stage. The computer now has the insane ability, it can throw you from anywhere on the screen.
Game Gear
Blood Code: Enter blood mode by pressing 2, 1, 2, DOWN, then UP at the Code of Horror screen. If done correctly, the words, "Now Entering Kombat" will flash on the screen, activating the blood code.
Game Boy
Play as Goro: To play as Goro, you must first defeat the game normally. Now sit back and watch the credits. When "The End" appears, hold Up + Left + Select + A. Enter your initials and press A.
Codes courtesy of IGN Codes