Cheat Mode:
Press ~ during game play to display the console window. Then, quickly enter one of the following codes to activate the corresponding cheat function.

Effect	Code
All weapons	gimmiegimmiegimmie
Cycle five chase camera angles	chasecam
Cycle four player classes	cycleplayerclass
Extra armor and health	nextarmor
Fly mode	spectator
God mode	invuln
Health debug mode	debug1
Less armor	prevarmor
Spawn indicated item	give <item name>
List items for give code	give
List console commands	listcommands or set
Next monster	nextmonster
No clipping	noclip
Previous monster	prevmonster
Restart level	restartlevel
Toggle monster targeting	notarget
Weapon debug mode	debug2
Unknown	cameralock

Item names:
Use one of the following entries with the give code.

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

Hidden surprise:
Load the game, then move the pointer over the clown's nose and press the Left Mouse Button when the circus music begins to play.