Get a kill with every gun in the game to unlock the shooting gallery, where you can test out all of the game's guns.

Head to the War Room from the Main Menu. Choose Options, and enter this code at the password screen to unlock Survival Mode: SELECT, L, R, SELECT, Y, Y, X, R, L, X, R, Y. This will not be saved if you turn off the game.

Beat the game on the hardest mode to unlock Survival Mode permanently.