Some cheat codes:
 From the console type these:
 
 FLY - Enable 'Fly Mode' [tap space to fly]
GOD - Gives you God Mode
 IMPULSE 9 - All Weapons and the Silver & Gold keys
 IMPULSE 11 - Get a Rune
 MAP ExMy - Goto Episode 'x' and Map 'y'
 NOCLIP - Enable 'No Clipping' Mode
 NOTARGET = enemys can't see you but if you attack them then they can see you
 
 To get the NIGHTMARE skill level:
 Well it seems that id did a good job of hiding the NIGHTMARE skill
 level. As yet I have not found out why they hid it because it is not
 much harder than the HARD skill level.  At any rate, if you want to
 see it, here's how you get to it.
 
 [BTW: Cheat codes DO work in NIGHTMARE]. 
 
 Go in any of the skill halls, it doesn't matter which.  Then goto the
fourth episode.  Once you fall in the water pull back until you move
 backwards and begin to descend again.  You will then be on a wood
 platform. On the left wall there should be a door the platform leads
 to, go in it and you find the NIGHTMARE skill level.  You are then
 brought back to the episode selection stage.  This does work on the
 Shareware version as well.
 
 
 Editing Tips:
 The savegames are in text format if you haven't figured that out
already. You simply need to find the variables that say ammo.shotgun