Launch the game with these command-line parameters
to activate cheat modes:

-mumford - Hodspodkins Mode
-whostayedlate - Rockhard Mode
-whostayedlateagain - EasterEgg Mode

Example:
"C:\Expend\go.exe" -whostayedlate

While in the game, you may enter these commands
followed by the "-" key on the numeric keypad:

Code .............. Result
bod ............... Enable Cheat Mode
mrbenn ............ Skip Level
zippy ............. God Mode
bucketofchicken .. Behind View
babapapa .......... Extra Credits
crystaltips ....... Extra Life
dunky ............. Instant High Score
albertofrog ....... Grenade Power-Up
bing .............. Disable Cheat Mode