Some "Combat Codes" (number of time you have to press the buttons):

P1(100)P2(100) - No throws
P1(020)P2(020) - No block
P1(987)P2(123) - Invisible time and energy meters
P1(033)P2(000) - Half energy Player 1
P1(000)P2(033) - Half energy Player 2
P1(707)P2(000) - Quarter energy Player 1
P1(000)P2(707) - Quarter energy Player 2
P1(688)P2(422) - Dark fighting
P1(985)P2(125) - Changing characters
P1(460)P2(460) - Dark fighting and changing characters
P1(466)P2(266) - Unlimited run
P1(642)P2(468) - Play Galaxian
P1(969)P2(141) - First Round winner fight against Motaro
P1(769)P2(342) - First Round winner fight against Noob Saibot
P1(033)P2(564) - First Round winner fight against Shao Kang
P1(205)P2(926) - First Round winner fight against Smoke
P1(282)P2(282) - View a message

Use these commands to start the game:

MK3 603015 Slow motion
MK3 8000 Turbo mode
MK3 12345 Tall characters
MK3 54321 Miniature characters
MK3 1111 Miniature characters that float
MK3 8888 Jumbo characters
MK3 1995 Invisible Kombat
MK3 831 Characters turn invisible
MK3 9966 Mirror mode
MK3 0666 Smoke enabled
MK3 1000000 Shao and Monty enabled (only in 2 player mode)