Create a new player with the following name: <name>CHEATER (for example,johnCHEATER). Note: The "CHEATER" part is case-sensitive. This will enable cheat mode and unlock all levels. Activate the following cheats by pressing the corresponding keys:
CHEAT FUNCTION - KEY 99 grenades; press F (default) to throw them - F2 Unlimited ammunition - F4 God mode - F5
To easily clear levels, run backwards in a large circle around the map while facing the monsters chasing you and shooting the ones closest to you as they follow. If they get too close or you need to reload, face the other way and keep running forward in the large circle. Note: You will run faster going forward. Then, turn around and continue to blast them.