Go to the options screen and highlight the "Continues" selection. Then, hold Block + Run until the word "Outstanding" is spoken and the cheat menu appears. There will now be four options to choose from:
Play as Meat
Enter "Group Mode" and beat the game with all sixteen characters. Then, after this has been accomplished, select any character and begin a match. Now your character will play as Meat with all the moves of the character that was selected.
Play as Goro
Beat the game with Shinnok. Then, change Shinnok's costume and select the invisible icon at the bottom of the character selection screen. Now press [Up] [Up] [Up] [Left] to highlight Shinnok's icon, then press [Run] + [Block].
Play as Noob Saibot
Beat the game with Reiko. Then, enter the Kombat code 012 012 in versus mode. Now exit this match and go to the character selection screen. Select the invisible icon at the bottom of the character selection screen. Press [Up] [Up] [Left] to highlight Reiko's icon, then press [Run] + [Block].
On the character selection screen, press [Start] + any button to rotate the select screen pictures two times to enable each character's second costume, except for Sonya and Tanya. The select screen pictures must be rotated three times for those characters.
Enter "Kombat Theatre" mode, highlight the desired character, and press [Block].