Level Passwords:
Use the code passwords in the Incredible! difficulty setting.

Code - Result
XL9ZMD - Tutorial (Stage 0-2)
G!G1DK - Giant Robot Factory 1 (Stage 1-1)
DXY6FK - Giant Robot Factory 2 (Stage 1-2)
BBT7FK - Giant Robot Factory 3 (Stage 1-3)
ZPGVFK - Blizzard Backdoor 1 (Stage 2-1)
B94GFK - Blizzard Backdoor 2 (Stage 2-2)
J2B?FK - Blizzard Backdoor 3 (Stage 2-3)
QF1XFK - Corruptorator 1 (Stage 3-1)
SW3!FK - Corruptorator 2 (Stage 3-2)
QQ?7DK - Corruptorator 3 (Stage 3-3)
24NCGK - Underminer (Stage 4-1)