From Dustin's Sega Saturn Page
FreePlay Mode
Okay, this time it really works. DO the following codes on the purple skeleton screen. Up, Up, Right, Right, Left,, Left, Down, Down; or Up, Up, Left, Left, Right, Right, Down, Down. If you did it correctly a voice should say "Excellent" Then wait for the menu's and don't push any buttons. Either of these codes are supposed to put you in freeplay mode.

Hidden Character Codes
These codes are presented in the following button order, X, Y, Z, A ,B ,C. Also note that they are to be enetered in a 1 player game after you loose or choose not to continue.
Mileena - 7, 0 ,0 ,7 ,2 ,3
Classic Sub-Zero 7, 6, 0, 5, 2, 0
ERMAC - 9, 6, 4, 2, 4, 0

Play Human Smoke
Player 1: After selecting the robot hold Left+HP+BLOCK+HK+Run

Player 2: Use the above code but substitute Right for the Left.

Shao Khan's Treasure
The first 10 are avaiable at different difficulty leves, the lats two are available when your win an 8 person tournament or beat Shao Khan on the 4th Tower (Path Select).
1 (Dragon) Outcome
2 (MK) Play Galaga
3 (Yin Yang) Fight Ermac
4 (3) Fight Noob Saibot
5 (?) Random
6 (Lightning Bolt) Fatality Demo 1
7 (Goro) Fatality Demo 2
8 (Raiden) Fatality demo 3
9 (Shao Kahn) Fight Noob Saibot and Ermac
10 (Skull) CLassic Match
11 (?)Mega Endurance Match
12 (?) Suprme Demo

Random Select Call
Hold up and press start for the random character select.

Some Kombat Kodes
300-003 - PUB! D.K.P.
200-002 - P.A.B

Change the opening quote
While Shoa Kahn is laughing on the purple skull screen press down, up, left, left, A, right, Down. It should change the opening quote from "There is no knowledge that is not power" to "Imagination is mor important than knowledge".

Crispy
Do the pit fatality in Hell then hold down both (on both controllers ?) HPs and Blocks and Shao Khan will say "Crispy". Then hold hold both HPs or both Blocks and he'll say it differently.

Extra treasures of Shao Kahn
If you beat the game on 2nd Master Mode and get to the treasures of shao Kahn go to the last one on the right and now push right one more time for more treasures!

Additional VS Kombat Kodes
390-000 Player 1 inflicts half damage
000-390 Player 2 inflicts half damage
390-390 Both Players inflict half damage
722-722 Combo System Enabled
321-789 Super Run Jumps
555-556 Special Moves Disabled
688-433 Quick Uppercuts
040-404 Real Kombat
024-689 Super Endurance
975-310 Regenerating Powerbars

Smoke Morph for Shand Tsung
Back, Back, Down, LK (do this fast)

Ultimate Code (Debug Menu)
At the title screen hit C,Right shift, A, Z, Y, C, Y, Right shift, A, X ( Crazy Cyrax)

Hit Up on the main options to reveal the ? The following options should be available

Free Credit
Mileena
Classic Sub Zero
Fatality time
One round matches.

65,535 Kredits
Start a 1 player game. Let the computer defeat you through all 5 original kredits. Just after losing the second fight of the 5th match, push START on controller 2. This will take you to the play mode screen. Let Shao Kahn laugh 3 times at this screen and you will automaticaly be entered into the first option, Mortal Kombat. If you die in any subsequent match, you will notice that you have 65,535 kredits when the continue screen comes up.