Bonus Robot

At the title screen, quickly press A, B, B, A, X, Z for a secret robot.

Level Select

At the title screen, quickly press Up, Up, Up, Down, Down, Down, A, B, C, X, Y, Z.

Note: You must have a six-button controller to enter this code.

Cheap Missile Launcher

At the Weapon Select screen, choose chain gun ($0) for the right arm and choose hammer knuckle for the left arm. Then choose the flying mine (you must have $800.) When you enter into the game, instead of having flying mines, you will have missile launcher.

Loads of Cash

At the title screen, enter a, b, b, a, x, z. Then, go to the options screen and select the easy difficulty. After that, play the first two missions normally, on the 3rd mission, kill as many robots as you can (but not the boss), then die on purpose. When you go to the weapons selection screen, you should have about $3,500 - select the following: Laser, Grenade Cannon, Extra Armor, and Flying Mines. When you go back, kill the boss using only your laser. When you go back to the weapons selection screen, you should have at least $61,000.