Unlock ALL Costumes in One Playthrough:
When you reach the 'Mercy Kill Mom' video sequence save the game and do not overwrite it. Continue until you complete the game. Start a new game and save it as another file. Return to the 'Title' screen and load the saved game file before the 'Mercy Kill Mom' video sequence. This time, try to unlock another costume. Complete the game again, then save it as another file. You can overwrite the new saved game file, but never the saved game file before the 'Mercy Kill Mom' video sequence. Begin a new game again. Notice that another costume was unlocked. Keep repeating the process until you have unlocked ALL of the costumes.
Go back to the walls where you jumped an iron fence when you have passed the point in the story where Travis has attacked Ellie with a chainsaw. There you will find the key to Room 301 which is located in the underground area. Inside Room 301 you will be able to recover ALL the weapons you obtained along with a med pack, health drink, and ammunition.
Unlock Young Alex Costume:
This costume will become availailable when ALL the other costumes have been unlocked.
At the 'Press Start' screen enter the code Up, Up, Down, Down, Left, Right, Left, Right, O. If you have input the code correctly you will hear a confirmation sound of a page turning and the young Alex costume will be be an available option.
Complete the game under the indicated condition to view the corresponding ending.
Unlock Good Ending:
Forgive Alex's father and show his mother mercy by killing her.
Unlock Drowning Ending:
Do not forgive Alex's father and show his mother mercy by killing her.
Unlock Hospital Ending:
Forgive Alex's father and do not kill his mother.
Unlock Bogeyman Ending:
Do not forgive Alex's father, do not kill his mother and do not save wheeler.
Unlock UFO Ending:
Do not forgive Alex's father, do not kill his mother and then save wheeler.
Unlock Alternate Costumes:
When you beat the game with the following endings the corresponding costume becomes unlocked.
Unlock Trucker Costume:
Get the 'Good' ending.
Unlock Deputy Costume:
Get the 'UFO' ending.
Unlock Order Soldier Costume:
Get the 'Drowning' ending.
Unlock Orderly Costume:
Get the 'Hospital' ending.
Unlock Bogeyman (Pyramid Head Helmet) Costume:
Get the 'Bogeyman' ending.
Unlock Extra Weapons:
The following two weapons can be found at the indicated location when you have beaten the game once.
Unlock Circular Saw:
This weapon which is used by Curtis is found in the garage at the Shepard's family home.
Unlock Laser Pistol:
Found in Joshua's room on top of his foot locker.