Level select
While playing the game, press Left(4), L1, Right(4), R1 to unlock all levels.
Restore health
While playing the game, press Up(2), Down(2), Left, Right, Left, Right, Circle, X to spawn a medpak that will restore 25 points of health.
Refill ammunition for current weapon
While playing the game, press Triangle, Circle, X, Square, R1, Triangle, Square, X, Circle, R1 to spawn an ammunition cartridge for your current weapon.
No clipping mode
While playing the game, press Up(3), L1, Up(3), R1, Up(2).
Enemies do not target you
While playing the game, press Down(3), L1, Down(3), R1, Down(2).
Hidden pumpkins
Set the system date to October 31. After you are ambushed by Hunters and Combine at a big house, drive along the road. Near where the supply cache is found, you will see an old truck. Go up to it, and there will be lots of pumpkins lying on the ground.
Lost reference
When you enter the White Forest base, you meet a Vortigaunt in a lab coat named Uriah. When you first enter the room where you meet Uriah, there is a gas tank against the back wall. Behind that tank is a small room with a computer that has a sequence of numbers on it. This is a reference to the TV show Lost that Gabe Newell added due to the fact that he and the creator of Lost were close friends.
