Cheat Codes: Activate the following cheats by entering the corresponding codes at the title screen. Note: These work on both PC and Mac:
CHEAT FUNCTION - CHEAT CODE invincibility - UP, DOWN, UP, DOWN, LEFT(2), RIGHT(2) plays a secret chiptune -LEFT, RIGHT, LEFT, RIGHT, LEFT, RIGHT, LEFT, RIGHT, shows FPS rate on the screen - DOWN(4), LEFT(4), RIGHT(4) unlocks all the levels - UP(3), DOWN(3), LEFT, RIGHT
Spread gun: In v1.1 or later, play the first mission and use the fence at the start to reach the watch post platform directly next to it. Once there, jump and shoot upward a couple times. A hidden power-up for the Spread gun will drop.