First create a game shortcut on your desktop (if you don’t have one). Right click on it, go to Properties, then add the line ‘-debug’ to the target box. Start the game and open the console with the ~ (tilde) key and type one of the following codes:

Code
GIVEALLWEAPONS
THEONEDEADLYCREAUTUREEVERCREATED
FREAKOFTHEUNIVERS
SKULLCOLLECTOR
OBSERVER
LIGHT
timescale 0.5
motiontrackerspeed 12
alienbot
marinebot
praetorianbot
predobot
xenoborg
 Effect
Give all weapons
God Mode (alien)
God Mode (marine)
God Mode (predator)
Toggle invisible mode.
Creates ambiance light.
Game speed. 0.0 to 0.1
Tracker speed. 0 to 16.
Spawn alien.
Spawn marine.
Spawn praetorian alien.
Spawn predator.
Spawn xenoborg.