Hello!
Reached the catacombs level and I just can't get past all these annoying mutants.
I'm having trouble implementing cheats. I'm playing with the FCAM 1.7 mod installed and the cheats don't seem to work.
I tried to run with -devmode command, editied the devmode.lua file but still nothing...
Any suggestions?
*EDIT - I actually managed to pass through the dreaded part. But the question still stands.
I hear the last level is simply too much too much...

Backup devmode.lua, and try this one: http://www.megaupload.com/?d=I0VZ0OXU.
Replace your existing one with this. Cheats are:

F1 - Toggles FirstPerson/ThirdPerson Camera Modes
F2 - Go to next checkpoint
F4 - No clipping on/off
F5 - Default Speed
F9 - Save Current Position
F10 - Load Current Position
F11 - Toggle Extra Information
o - Gives 999 ammo
p - Gives all weapons
BackSpace - Toggle GodMode
= - increase speed
- - decrease speed

Let me know if you have any luck.