Press [Tab] during game play, then type one of the following codes to activate the corresponding cheat function:

Effect	Code
999 of all ammunition types	allammo
External view	behindview 1
Normal view	behindview 0
Reset bad textures on walls or creatures	flush
Fly mode	fly
No clipping mode	ghost
God mode	god
Hide all monsters, weapons, and items	hideactors
Show all monsters, weapons, and items	showactors
Disable invisibility	invisible0
Invisibility	invisible1
Kill selected monsters	killall
Kill all monsters	killpawns
Level or server select	open
Disable timer	playersonly
Set game speed (1 is normal)	slomo