Custom Edition: Cheat Codes:
Note: These only work for the Custom Edition of Halo: Combat Evolved.
Open the properties window of the Halo shortcut and add ? -console ?devmode? after the target. Start the game with the -console -devmode command line parameter. Press ~ during game play to display the console window, then enter one of the following codes to activate the corresponding cheat:
CHEAT FUNCTION – CHEAT CODE
Toggle instant deaths for enemies that see player – cheat_medusa