Press Right, Left, Down, Up, L + R during game play.
Weapons For Health
Hold in L and R and press Triangle X Square Circle. You will Sacrifice All Energy and some Weapons but it will give a 15% Health boost when you need it the most
Various Cheats
You need to do these codes during gameplay. They'll work for everything, but multiplayer and online
Killer Weapons
Press X twice and Up twice and L & R together
Mega Guns
X, Triangle, X, Triangle and L & R together
Infinite Weapons
Triangle, Triangle, Down, Down and L & R together
Energy Attacks
freeze-up, down, up
plant bomb-down, right, up, left, down
invisibility-left, left, down, down
shield-right, right, down, down
Unlockable character and Extra Levels
Axel
beat Russia Mini Level
Hammerhead
Beat Tokyo Rooftop mini level
Mr. Slam
Beat L.A. mini level
Cousin Eddy
Beat L.A. - Cousin Eddy stage in Story mode
ATV
Beat L.A. - Cousin Eddy stage in Story mode
Dark Tooth
Complete Story mode with any character
Crimson Fury
Complete the Monaco mini level
Extra Levels
Paris Deathmatch Level
Complete the Paris mini level
Egypt Deathmatch Level
Complete the Egypt mini level
Rose Deathmatch Level
Complete the Rome mini level
Tokyo Streets Deathmatch Level
Complete the Tokyo Streets mini level
Unlock Tower Tooth for Endurance and Challenge Modes
Quite simple: To Unlock Tower Tooth, finish story mode with 5 different vehicles. Tower Tooth will be unlocked for one Endurance mode match and one Challenge mode match.