Open the console with pressing [~] and type in:

 Invuln                     God mode
 GimmieGimmieGimmie         All weapons available
 NoClip No                  Walk / fly thru walls
 NoTarget                   Invisible ON/OFF
 Spectator                  Fly mode
 ChaseCam                   Change camera angle (5 possible angels)
 CyclePlayerClass           Cycle through 4 player classes
 NextArmor                  Refresh armor and health
 PrevArmor                  Decrease armor
 NextMonster                Find next monster
 PrevMonster                Go to previous monster
 RestartLevel               Restart current level
 Give [Item][Amount]        Get items where [Item] might be

                            AirAmmo
                            AngelCharm
                            BeastClaws
                            Belt
                            BlackDiamond
                            BloodRose
                            Boots
                            ChaoHeart
                            CrystalBall
                            Draco
                            EarthAmmo
                            Fist
                            Galaxion
                            Gauntlets
                            Hawkeyes
                            Health
                            Key
                            MagmaAmmo
                            MagmaCannon
                            Pamphlet
                            PickupTrigger
                            Punisher
                            RageOrb
                            Scourge
                            SpiritLance
                            Stargaze
                            Thornblade
                            Ticket
                            Twister
                            WaterAmmo
                            Windblade
                            ZeroCannon

 Not known so far, but understandable

 CameraLock
 Debug1
 Debug2

 It seems some people have problems to activate the codes, sometimes
 you will have to activate a certain developpers mode. Open the file
 player.cfg in the \profiles\ folder and look for the line

 "Developer" "0"

 Change that "0" to "1" and start the game.

 In the game menu now choose the keyboard setup where you now have two
 more options 'hud toggles' and 'cheats' (at the bottom). Now you can
 bind these options to keys to have them handy in the game.

 Unfortunately you need to play that "0" <-> "1" game anytime you start
 the game, because the game resets that when exiting.

 ---

 Also in the .cfg file:

 Search for

 enabledevice "##mouse"

 Below this u might add a line that e.g. looks like this:

 rangebind "##keyboard" "W" 0.000000 0.000000 "Invuln"

 Save and start the game and from now on press [W] for God mode. Of cause
 this works with all cheats.