During the game, press the [~] (tilde) key to bring up the console, where you enter:
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God 1/0 – God Mode On / Off.
Health # – Set health to #
Invisible 1/0 – Invisible mode, on / off.
Mucha 1/0 – Pass through walls, on / off.
MuchaSpeed # – Set movement speed to #
DrawFPS 1/0 – Show FPS, on / off.
FOV # – Set FOV to #