All levels and characters:
Start a new game and enter "Shooterman" as a case-sensitive name to unlock all levels and characters.
At any menu screen, hold L1 and press Circle, Triangle, Circle, Triangle, X.
All FMV sequences:
At any menu screen, hold L1 and press Circle, Square, Triangle, Circle, Square.
Big head enemies:
At any menu screen, hold L1 and press Circle, Square, X, Circle(2
Control character selection screen:
At the character selection screen, press Left Analog-stick Left and Left Analog-stick Right to move the portraits in the corresponding direction.
Play as Luger:
Beat Mission 2 in story mode to unlock Luger.
Play as Rico:
Beat Mission 3 in story mode to unlock Rico.
Play as Hakha:
Beat Mission 4 in story mode to unlock Hakha.
Switch Guns Quickly:
While sprinting, release the button. As soon as you do that, switch your gun. The next gun will automatically appear in your hands.
Press Reload, switch the gun, then immediately switch back to your original weapon.
Shoot 3 Shotgun Shells:
When using the shotgun, it has two modes of fire (regular shoots one shell, alternate shoots two shells). By pressing both fire buttons, you will shoot three shells, which in most cases is more useful. Try using this on groups or stronger enemies.
Loads of Shotgun Shells:
Go and collect a shotgun but make sure it has more than 8 bullets, and fire 1 bullet only! Then when you press reload, he will bring the shotgun up then down a little bit to re-load. As soon as he brings it down a little bit start walking forward and he should load more than one shell. If he does not and only does a couple more than one, just press re-load and he will load the rest of them. Then just keep collecting shells and keep re-loading. This will take a few trys, but it'll work when you get the hang of it.
Thanks to Revolution readers Eamon, Jordan, and Pezza Rights!