Level Skip:
Hold R1 + R2 + L1 + Select, and press , , , , , , , during game play. If done correctly, you will automatically win the match.

Pause in Multi-Player Mode:
Since the game does not have a pause option in the multi-player mode, simply press Start , highlight "Quit" and press . Your game will be paused, but it will not quit unless you select "Yes". To resume the game, select "No".

Hints

Rocket Jump:
Pick up a Rocket Launcher and switch to it, then point your gun straight down. Jump, and when you are at your highest point, quickly fire the Rocket Launcher. If done correctly, your character will go high in the air. Note: You will most likely lose a little bit of health while doing this, so be careful.

Bonus Characters and Level:
Beat the game in campaign mode under the "I Can Win" difficulty setting. A bonus level and two more characters will appear after the credits. Beat the bonus level to unlock it and the new characters in multi-player mode.

Pause in Multi-player Mode:
Since the game does not have a pause option in the multi-player mode, simply press Start , highlight "Quit" and press . Your game will be paused, but it will not quit unless you select "Yes". To resume the game, select "No".

Easily Kill Vadrigar:
This very tough boss can be killed easily. When the level starts, dart forward and aim (get railgun first) at the beams coming from the wall. Destroy 2 of the 3. Then when you are pefectly lined up on the 3rd switch to the BFG and fire it into the nearby tunnel. Either jump over the red line or dodge the grenades. You'll reach the end of the tunnel and find either health or armour. If you're now in the health tunnel get against the far wall. Slowy sidestep out whilst zooming youu will see a purple sphere with a quake symbol wrapped around it. This is the invulnerability item. Run out to the right turn around and look down and bfg jump! It is tricky to do but you'll get the hang of it easily. When you are up there get the invulnerability item and move slowly towards the edge look down and you should see quad damage. Get it make sure your weapon is the bfg and hit it and spin around in circles releaseing a constant storm of bfg rockets and when you hear that blink sound when you hit some one, concentrate your fire on Vadrigar. He should take about 3 shots then you have completed the game.....or have you? The answer to that question is: No you get an extra level with two more characters beat that level and you SHOULD get it on multiplayer mode.

GameShark Codes

Master Code (must be on) 
ECBB8E64 1456E60A

Max Machine Gun Ammo
4CFF0730 1456E404

Max Shotgun Ammo 
4CFF0734 1456E404

Max Plasma Gun Ammo  
4CFF0748 1456E404

Max Chain Gun Ammo 
4CFF075C 1456E404 

Max Grenade Launcher Ammo 
4CFF0738 1456E404

Max Rocket Launcher Ammo    
4CFF073C 1456E404

Max Frag Medals 
4C002DEC 1456089C

Thanks to Revolution readers Roberto, Mentalmaniac, Matt Briggs and The Doctor.!