30 Kredits
Press Back, Up, Forward, Down, Back, Select at the Select Screen.

Disable Throws
After choosing your fighters in two player mode,
immediately hold down and High Punch when the portrait screen appears.
At the beginning of the round, it should say "Throwing Disabled".

Extended Fatality Time
Press Up, Up, Back, Up, Down, Select at the Select Screen.

Fight Jade
Press Up, Down, Down, Back, Forward, Select at the Select Screen.
Or win at least one round on the stage before question mark, using only Low Kick. Block cannot be used either.

Fight Kintaro
Press Up, Down, Down, Forward, Forward, Select at the Select Screen.

Fight Noob-Saibot
Press Back, Up, Down, Down, Forward, Select at the Select Screen. Or win 50 matches in a row.

Fight Shao Kahn
Press Up, Up, Forward, Back, Select at the Select Screen.

Fight Smoke
Press Up, Back, Up, Up, Forward, Select at the Select Screen.
Or do uppercuts on the Portal Stage,
until Dan "Toasty" Forden's face appears in the lower right corner.
Hold down and keep pressing start.

Four Character Tournament
At the start screen, hold down L and R and press Start.
You will be at a screen that will let you and your opponent select four characters for a long endurance round.

Game Genie Codes
C2C4-47AA - Infinite continues
DF8C-CDDA - Start with 0 continues
D78C-CDDA - Start with 2 continues
D58C-CDDA - Start with 6 continues
DB8C-CDDA - Start with 8 continues
C2B1-14F7 - Player 1 is invincible
DDB5-1FF7 - Player 2 or computer is killed by one hit
C2B5-14F7 - Player 2 or computer is invincible
DDB1-1FF7 - Player 1 is killed by one hit
622B-C7AC - Disable throws--2-player mode
6DC7-1DAA - Infinite time
06E1-17D4 - Mileena's Sai Throw does massive damage
06E9-1DD7 - Liu Kang's High Fireball does massive damage
06E2-1767 - Kung Lao's Hat Throw does massive damage
06EF-4767 - Cage's Shadow Kick does massive damage
06EB-17AF - Reptile's Force Ball does massive damage
06E0-4FA4 - Shang Tsung's Flaming Skull attack does massive damage
06E9-17A4 - Kitana's Fan Throw does massive damage
06EE-C4A4 - Baraka's Blade Spark does massive damage
06E4-34DF - Rayden's Lightning Bolt does massive damage

For the rest of the codes, 1-player only, can't see the ending
CBC6-3D6E + DDC6-3DAE - Always fight Kung Lao
CBC6-3D6E + DFC6-3DAE - Always fight Liu Kang
CBC6-3D6E + D4C6-3DAE - Always fight Cage
CBC6-3D6E + D7C6-3DAE - Always fight Baraka
CBC6-3D6E + D0C6-3DAE - Always fight Kitana
CBC6-3D6E + D9C6-3DAE - Always fight Mileena
CBC6-3D6E + D1C6-3DAE - Always fight Shang Tsung
CBC6-3D6E + D5C6-3DAE - Always fight Rayden
CBC6-3D6E + D6C6-3DAE - Always fight Sub-Zero
CBC6-3D6E + DBC6-3DAE - Always fight Reptile
CBC6-3D6E + DCC6-3DAE - Always fight Scorpion
CBC6-3D6E + D8C6-3DAE - Always fight Jax
CBC6-3D6E + DAC6-3DAE - Always fight Kintaro
CBC6-3D6E + D2C6-3DAE - Always fight Shao Kahn
CBC6-3D6E + D3C6-3DAE - Always fight Smoke
CBC6-3D6E + DEC6-3DAE - Always fight Noob-Saibot
CBC6-3D6E + FDC6-3DAE - Always fight Jade

One Hit Danger Mode
To enter one hit danger mode at the character selection screen hit down, up, right, up, left, select.
if it is correct you will hear a sound.

Random Select
Press Up + Start at the Choose Your Fighter screen.
Be sure to have the selector positioned where it originally appears.

Spike Slide
Immediately after you uppercut your opponent into the spikes, hold down on both controllers.

Super Strength
Press Down, Up, Forward, Up, Back, Select at the Select Screen.

Tournament Mode
You can hold button L and button R on and then press start on the menu screen.
One thing I found is that if you hold start on the screen and press A,
the computer will select your opponent for you.
And then there is the "?",
The ? simply means that you won't find out which character the computer chose for you,
until he/she actually pops up in battle.
You can also use Random Select in this Mode.