Unverified. Hold L + R on the main title screen and a cheat menu will appear. Enter the number codes for the following.

141421 ... Unlock all monsters/stages.
082864 ... Unlock all stages.
082864 ... Demo/attract mode.
874098 ... Same as demo/attract but only summary screens are seen.
071767 ... Buildings die in one hit.
986960 ... Your player is invulnerable.
11235 ... Your player has all upgrades.
66730# ... # is integer for cutscene.
314159 ... Shows version number.
000000 ... Resets all cheats to default off.