Buck Bumble

Invincibility
Go to the title screen and press the following button combination:
Hold Z and press R, R, L, L, Up, Down, Left, Right.
If the code is accepted you should hear a sound.

Select any stage:
Go to the title screen and press the following button combination:
Hold Z and press Right, Down, Down, Right. Release Z button, then hit
Right, Up, Down, Left, Left, Up, Right, - Right. If the code is
accepted, you should hear a sound.

Maximum ammo, health and all weapons:
Go to the title screen and press the following button combination:
Left, Right, Up, Down. Then, hold Z and press Right, Right, Left, Left.
If the code is accepted, you should hear a sound.
Then during the game play, hit A + B + R

Unlock Dark Stinger as playable character:
Hold Z + Analog-joystick Up and press C-Up, C-Right, C-Down,
C-Left(5 times), B, A, B just before the opening screen appear.
If the code is accepted, you should hear a sound.

Faster text scroll
Press Z to scroll the text.

Bypass dialogues:
Press A