If you want to challenge yourself then at the 'Character Select' screen hold 'Up' and press 'Start' on the following characters (depending on what player you are) to get a random character to use in the game.

Player-1:
Hold 'Up' and press 'Start' on Kitana.

Player-2:
Hold 'Up' and press 'Start' on Scorpion.

To enable these effects in the game Player 1 and Player 2 must enter the corresponding codes at the Vs. Screen. The order that the codes are entered is B-R-A (LP-BLK-LK).

Unlock Infinite Run
Player 1: 4-6-6
Player 2: 4-6-6

Play in Kahn's Kave
Player 1: 0-0-4
Player 2: 7-0-0

Play on the Pit 3
Player 1: 8-2-0
Player 2: 0-2-8

Play on Jade's Deset
Player 1: 3-3-0
Player 2: 0-3-3

Play on Kahn's Tower
Player 1: 8-8-0
Player 2: 2-2-0

Play on Rooftops
Player 1: 3-4-3
Player 2: 3-4-3

Play on Scislac Busorez
Player 1: 9-3-3
Player 2: 9-3-3

Play on Subway
Player 1: 8-8-0
Player 2: 0-8-8

Play in the Kombat Temple
Player 1: 6-0-0
Player 2: 0-4-0

Play on the Belltower
Player 1: 0-9-1
Player 2: 1-9-0

Play on the Bridge
Player 1: 0-7-7
Player 2: 0-2-2

Play on the Graveyard
Player 1: 6-6-6
Player 2: 3-3-3

Play on the Street
Player 1: 0-7-9
Player 2: 0-3-5

Play Scorpions Lair
Player 1: 6-6-6
Player 2: 4-4-4

Unlock Silent Kombat
Player 1: 3-0-0
Player 2: 3-0-0

Throwing Disabled
Player 1: 1-0-0
Player 2: 1-0-0

Play on the Waterfront
Player 1: 0-0-2
Player 2: 0-0-3

Throwing Encouraged
Player 1: 0-1-0
Player 2: 0-1-0

Play in the Soul Chamber
Player 1: 1-2-3
Player 2: 9-0-1

Play on Noob Saibot Dorfen
Player 1: 0-5-0
Player 2: 0-5-0

Unlock Unikoriv Referri: Sans Power (1HKO)
Player 1: 0-4-4
Player 2: 4-4-0

To unlock Bo Rai Cho the drunken master and Kabal the Black Dragon Warrior you have to perform the following tasks in the game.

Unlock Bo Rai Cho:
Get a score of at least 19,000 points

Unlock Kabal:
Break at least 3 chains.

To unlock this former member of the Lin Kuei clan select Robo Smoke and just before the battle begins press and hold Block + Run + High Punch + High Kick + Back. If you have entered the code correctly you will see smoke flaming into Human Smoke.