Battle mode:
Save the game at least one time. Hold X + Y + Z + Start on controller two at the title screen. The words "" will be spoken to confirm correct code entry. Press Start on controller one. An option for Battle mode will now be accessible. The objective of "Battle mode" is to enter a secret zone after killing all enemies with all weapons at your disposal.

Alternate clothing:
Start a new game and choose either character. Hold L + R on controller two when "June 1998" is displayed on the opening screen. Jill and Chris will be wearing alternate clothes when game play begins.

Rocket launcher:
Complete the game with a time that is under three hours. Replay to game to access the rocket launcher with unlimited ammunition.

Hint: Killing Plant 42:
Chris can save ammunition when fighting Plant 42 by using the combat knife. Only about a dozen hits with the knife are needed to kill it.