In single player games, press Start to pause game play, then hold L + R and press A, B, A(2), B(2), A(2). You will advance ten levels, depending on the current level.
All weapons, items, keys
Press Start to pause game play, then hold L + R and press A, B(2), A(5).
Berserk
Press Start to pause game play, then hold L + R and press B, A, B, A(5)
Computer map
Press Start to pause game play, then hold L + R and press B, A(7)
Disable God mode
Press Start to pause game play, then hold L + R and press A(2), B, A, B(4).
God mode
Press Start to pause game play, then hold L + R and press A(2), B, A(5).
Invincibility
Press Start to pause game play, then hold L + R and press B(3), A(5)
Level skip
In single player games, press Start to pause game play, then hold L + R and press A, B, A(2), B(3), A.
Radiation suit
Press Start to pause game play, then hold L + R and press B(2), A(6)
Advance ten levels...