Level select
Pause the game and press Right, Left, R2, R1, Triangle, L1, Circle, X. If you entered the code correctly, a menu will appear in the top half of the viewing window. Press Left and Right to select a level, and confirm your entry with Square, Circle, Triangle, or X.

Invincibility
Pause the game and press Down, L2, Square, R1, Right, L1, Left, Circle. If you entered the code correctly, a message will appear on the bottom of the viewing window and will disappear the game is resumed. Your character will be invincible, however unlike the invulnerability power-up, your screen will not turn white.

Weapons, ammunition, and keys
Pause the game and press X, Triangle, L1, Up, Down, R2, Left(2). If you entered the code correctly, a message will appear on the bottom of the viewing window and will disappear the game is resumed. All weapons, ammunition for them, and keys for current level will be available.

Map all lines
Pause the game and press Triangle(2), L2, R2, L2, R2, R1, Square. If you entered the code correctly, a message will appear on the bottom of the viewing window and will disappear the game is resumed. All walls and boundaries will appear on the map for the current stage.

Map all items
Pause the game and press Triangle(2), L2, R2, L2, R2, R1, Circle. If you entered the code correctly, a message will appear on the bottom of the viewing window and will disappear the game is resumed. All objects including enemies, items, weapons, and secret switches will appear on the map as blue triangles.

X-Ray specs
Pause the game and press L1, R2, L2, R1, Right, Triangle, X, Right.

Transparent walls
Pause the game and press L1, R2, L2, R1, Right, Triangle, X, Right. Now your character may now see through one layer of wall or sprites.

Random levels
At the password screen, enter "DOOMMNLxxx", where xxx the same character such as !!! or 555. Now the game will start at a random level with an unusual amount of ammunition, armor, and life.

Play in linked mode with only one disc
Note: Sony does not recommend removing a spinning disc from the Playstation. Connect two Playstations with the linkcable, and power on both systems. Begin Doom on Playstation 1. Select Deathmatch or a cooperative game. Playstation 1 should try to connect to Playstation 2. Wait a few seconds, remove the disc from the Playstation 1, and start the game on Playstation 2. Enter all selections identically to Playstation 1 and begin playing.

The game will hang from time to time. At these points, swap the disc to the other Playstation after waiting a few seconds before removing the disc.