Cheats / Codes for Mortal Kombat 3

Access Smoke, Bosses, and Hidden Game: (unconfirmed)
Source: GamePro - February 1996 - Page 117
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At the Start Game/Options screen, press Button C, Right, A, Left, A, Up, C, Right, A, Left, A, Up.  Now you can access Smoke, the bosses, and even play a hidden game.

Cheats and Play as Smoke: (unconfirmed)
Source: GamePro - February 1996 - Page 118
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Cheats: At the Start Game/Options screen, press Button A, C, Up, B, Up, B, A, Down.  The cheats option will appear, giving you more continues, a sound test, and a bio screen for each character.

Play as Smoke: At the MK3 logo, press Button A, B, B, A, Down, A, B, B, A, Down, Up, Up.  The screen will turn red.  Now, at the Select Your Fighter screen, you can select Smoke.

Secrets Menu: (unconfirmed)
Source: GamePro - February 1996 - Page 118
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At the Start Game/Options screen, press Button B, A, Down, Left, A, Down, C, Right, Up, Down.  A secrets option will appear.  Now you can turn the timer off, see each character's win screens, and pick your Kombat zone.

Endurance Match: (unconfirmed)
Source: GamePro - February 1996 - Page 116
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At the Start Game/Options screen, simultaneously hold Button A, B, C and press START.  You'll enter an Endurance mode where four players can battle it out.

Game Genie Codes
Source: GamePro - May 1996 - Page 108, July 1996 - Page 120
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DM2A - JA3Y - From the main menu, press Button A, B, or C twice to bring up each of the three secret menus.
C5ZT - GA28 - Player One takes all damage
BWXT - KA62 - First fight for Player One is against Shang Tsung
B8XT - KA62 - First fight for Player One is against Motaro
HW1T - KAA4 + BW1T - JAA6 - All fights after the first are against Shang Tsung
HW1T - KAA4 + B81T - JAA6 - All fights after the first are against Motaro
AMZT - GA5E - Both players take no damage
B4XT - KA62 - Player One's first fight is against Smoke
CGXT - KA62 - Player One's first fight is against Noob Saibot
HW1T - KAA4 + B41T - JAA6 - All fights after first fight are against Smoke
HW1T - KAA4 + CG1T - JAA6 - All fights after first fight are against Noob Saibot