Cheat Mode
Press [~] while playing to bring down the console, and then type in the following codes:
sv_everything_1 - All Weapons and ammo.
sv_demon_1 - Demon Mode.
sv_cheat_godmode_1 - God Mode.
sv_max_ammo_1 - Max ammo.
sv_max_health_1 - Max Health.
sv_perfect_finish_1 - Finish the level at 100%