Access the Options menu, then select Continue Options and hold block+run for about 10 seconds. You can now fiddle with the cheat options -- one at a time.
Play as Goro

    Select the Hidden button on the character select screen, then move up three, over one to Shinnok, and press block and run.
Play as Meat

    In order to play as the character MEAT you must go to "GROUP MODE" which can only be played in a two player mode. Play every character in the game (16 in all) and make sure you win every time. After you play and win with the final character you can pick anyone, your character will then be MEAT. He will have all the moves of the character you selected but will look like a bloody skeleton.
Play as Noob Saibot

    Select the "hidden" button on the character select screen and then move up two, over one to Reiko, and press block and run. (If you still haven't figured it out: Noob Saibot is "Boon/Tobias" backwards. Ed  Boon and John Tobias are the creators of Mortal Kombat)

    Here's a strange way to avoid an attack. Change characters just before a projectile attack reaches you, and it will pass right through you.
Exorcist Impact

    At the end of the Impact cinema sequence, you can rotate Impact's head with the control stick. Wait until it shows Impact's full body with the yellow and orange stripes, and then use the control stick to turn his head Exorcist style!
Reappearing Items(Lots of cash)

    If you find a room with a lot of gold (or pots with gold) such as the first room in Oedo Castle walk into the room and get the gold. Then leave and come back in and -- surprise! All of the gold is right back where it was! You can do this as many times as you want and stack up on cash.

    After you have beaten Nepty and have been transported back to Larapool, make your way back to the ferry that originally brought you there, get on the ferry and ride it three times. On the third trip, stay in the cabin and move up to the crates on the right. A "?" will appear over brian's head, signaling an invisible spirit element!
Full health at Inns

    To get full power without using items, go to an inn and say you will stay the night. Then, when at the saving screen, hit B to escape. You will now have full health.
Avoid some Attacks

    When an enemy casts a ROCK spell on you, start running directly towards them.You will take control of your character while the boulder is still in the air. If you can get close enough to the enemy, fast enough, the stone will pass harmlessly overhead.