Use ` to bring up the console window and use the codes from the list:

Code                     Result

please god               God Mode

please giveall           Give All Items

please killall           Kill All Enemies

please open              Open All Doors

please fly               Fly Mode

please ghost             No Clipping

please invisible         Invisibility

please tellall           Show All Messages from Netricsa

please refresh           Resets Health to 100