Debug Menu! PC version only.
This will open up new menus that will allow you to skip to any level, have invicibility and infinite ammo amoung lots of other cool things!
To enable these options open the Shadowman folder on your computer and locate this directory:
In that directory, find the files debug.msc and release.msc. Rename release.msc to release.old now rename debug.msc to release.msc. The next time you start a new game, the debug menu should become available.
NOTE: You can restore your original settings by changing the name of your new release.msc back to debug.msc, then renaming the release.old file to release.msc.