Doom Cheats
Invincibility                           iddqd  
All weapons, keys, ammo, and 200% armor idkfa 
Berserker strength                      idbeholds  
Temporary invincibility                 idbeholdv  
Temporary invisibility                  idbeholdi  
Full automap                            idbeholda  
Anti-radiation suit                     idbeholdr  
Light amplification visor               idbeholdl  
Walk through walls                      idspispopd or idclip  
Chainsaw                                idchoppers  
Level select                            idclev<episode number><map number>  
Toggle full map; full map and objects; normal map  iddt 
Display coordinates and heading         idmypos  
Change music to indicated level         idmus<level number>  

Duke Nukem 3D Cheats

Toggle God mode                       dncornholio  
God mode and unlimited jet pack       dnkroz  
All weapons, maximum ammo, all keys, all items  dnstuff 
Maximum armor, all keys, all items 	dnitems  
Use steroids, even if not in inventory dnhyper 
Level select (example: dnscotty309 for episode 3 level 9)  dnscotty<episode number x><level number xx>  
Push SPACE for money dncashman  
Alternate viewpoint dnview  
Display frame rate dnrate  
Change skill level dnskill<skill level 0-4>  
"Pirates Suck" message dnbeta  
"Register Cosmo" message dncosmo  
"Buy Major Stryker" message dnallen  
Walk through some walls dnclip  
All keys dnkeys 
All weapons and ammo dnweapons  
Display debug information dndebug  
Display coordinates dncoords  
Display entire map dnshowmap  
Toggle all doors dnunlock  
Display message dntodd  
Toggle monsters dnmonsters  
All inventory dninventory  
Level select values:
Submit the entries below with the dnscotty code.
 

101
102
103
104
105 (Boss)
106
201
202
203
204
205
206
207
208
209 (Boss)
210
211
301
302
303
304
305
306
307
308
309 (Boss)
310
311 

Maximum health and ammunition:
Remember when editing files to create a backup copy before you start to edit the file. Usin your text editor alter the "user.con" file in the game folder. Find the "MAXHEALTH" or "MAXPLAYERHEALTH" entry and change "100" to "9999". Find the "MAXAMMOFORPISTOLS 100" entry and change it to "MAXAMMOFORPISTOLS 500". Do the same for the other weapons in the file.
 

"Damn I'm Good" difficulty level God mode:
Start your new game at the COME GET SOME difficulty. Use the God mode cheat code and begin a new game under DAMN I'M GOOD difficulty. 

Opponent viewpoint:
Begin a modem multiplayer game and enable recording on the options screen. Press K during game play to view the game from your opponent's view point. 

Third person view of players 2 to 8 in demos:
Begin your game and hit F7. Push ESC and pick QUIT TO TITLE. You will now see players 2 to 8 from a third person view.