Doom

System: Playstation

Map all lines:
Pause the game and press Triangle(2), L2, R2, L2, R2, R1, Square. To confirm correct code entry, 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. To confirm correct code entry, 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.

Invincibility:
Pause the game and press Down, L2, Square, R1, Right, L1, Left, Circle. To confirm correct code entry, 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). To confirm correct code entry, 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.

Level select:
Pause the game and press Right, Left, R2, R1, Triangle, L1, Circle, X. If the code was entered 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.

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

Random levels:
Enter DOOMMNLxxx, where xxx the same character such as !!! or 666, at the password screen. The game will start at a random level with an unusual amount of ammunition, armor, and life.

Playing 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.