Three extra lives:
Press Up(2), Down(2), Left, Right, Left, Right, B, A at the title screen. Then, press Start to begin the game in single player mode or Select + Start to begin in two player mode.

Thirty lives per continue:
Press Up(2), Down(2), Left, Right, Left, Right, B, A before the demonstration begins at the title screen. Then, press Start to begin the game in single player mode or Select, Start to begin in two player mode.
Information in this section was contributed by Leon Noel and Christine.

Unlimited lives:
Press Up, Down, Up, Down, Left, Right, Left, Right, A, B, A, B, Select, Start when "Jungle" appears on the demonstration screen.

Transfer lives:
Begin game play in two player mode. Press A + B when losing a life to use a life from the other player.

All weapons:
Press Down(2), Up(2), Right, Left, Right, Left, A + B before the demonstration begins at the title screen.

Level select:
Press Up(2), Down(2), Left, Right, Left, Right, B, A, Start(2) at the main menu.

Expert mode:
Successfully complete the game and start another game. The new game will feature the same amount of lives at the end of the last game and more difficult opponents.

Alternate ending sequence:
Hold Select + Start during the ending sequence, but before the credits begin. Keep the buttons held until the credits end to see a message from Red Falcon.
Information in this section was contributed by nnicky.

Sound test (Japanese version):
Hold B + A and press Start at the title screen to display the sound test screen to hear the game's sound effects and music.

Hint: Shoot while crouching:
Crouch on controller one and press Up on controller two in the Base 1 or 2 levels.
Information in this section was contributed by liup.

Hint: Level 1: Cross bridges:
When you get to the bridges, jump on them while holding Right to get across.
Information in this section was contributed by AZMatt1.

Hint: To the ground below:
To go to the bottom part of the stage or in the water, crouch and press A.