Press the ~ key, then type the code. (Thanks to ALMEHDA@aol.com)

Effect	Code
All Weapons	IMPULSE 9
All Weapons, Mana, Items	IMPULSE 43
Fly Mode	IMPULSE 39
God Mode	GOD
Invisibility	NOTARGET
Mouse View	MLOOK
No Clipping	NOCLIP
Raise Level	IMPULSE 40
Restart Level	IMPULSE 99
Sheep	IMPULSE 14
Tome Of Power	IMPULSE 25
Torch	IMPULSE 23