First of all you must obtain all the hidden characters in the game. Go to the character select screen. Hold down the L1 and L2 buttons and select your character in the normal manner. Now your fighter will appear as a wire-frame model. When the fight starts, the view will change to a first-person perspective.

Purple Kazuya:

All the secrets characters must be accumulated first. Start a new game and highlight Kazuya. Now hold down Start while selecting him. He should now fight in his third, purple costume.

Thought Bubbles:

Play in practice mode. Leave your character alone for a while. You'll now see thought bubble appears above his or her head! Sky Mode: If, having obtained all of the secrets characters, you press L and Select when choosing a character, you will enable.

Sky Mode.

You must hold down this button combination until the fight actually starts, at which point you will hear a punch sound to confirm that the cheat has been activated. Basically it allows you to fight a la Mortal Kombat, with certain uppercut-type moves resulting in your opponent flying high up into the sky. For some strange reason it seems to work with sweeps as well. This particular cheat also enables Big Head mode.

Obtaining Kazuya Mishima:

Acquire all the sub-bosses by completing the game using the ten original fighters. Play through using a sub-boss. Once completed, Kazuya will beaded.

Fight Roger Or Alex:

Once you've got the Devil and Angel, start a new game with any character and when you reach the third fight, defeat your opponent on the last round with only a particle of energy left. If you do it right you will hear the word 'Great' and the next fight will be against Roger or Alex.

Devil Or Angel:

Complete the game with Kazuya. Now these two characters will be added.

Roger And Alex:

There's an easy way to get Roger and Alex. First ensure that all players are selectable. That includes Kazuya, Devil and Angel. Now all you have to do is go to practice mode and do one 10-hit combo with any character. Make sure that you turn off the tool bar at the bottom of the screen where you can see the buttons to press, otherwise it won't work. When it's activated, you should hear the word 'great'.

Get Roger and Alex Faster (no sub-bosses needed)

First turn on game, second go to arcade mode, third pick one of the original ten characters, fourth win round 1 then loose round 2 then with a little energy left then if you here the words "great" then the next fight you will fight either a lizard or a kangaroo (Alex or Roger) if you beat them you will automatically be able to use them!! to use 1 press triangle, to use the other press x (cross)

Big heads and even bigger heads!!
To activate big head mode choose your character and hold down SELECT until the bout begins.
To get even bigger heads and even bigger bodies just repeat this process at the continue screen in arcade mode or the player select in any other mode!
To get steel King & cool Suits for the characters
To get steel king:  beat the game with King
To get a cool uniform that the computers wear:
when you go to select a character make sure you press the triangle or circle button to select them and when you are a bout to fight, you will see the uniform.