In-game you can press [~] and enter the following string after
 the 'Omen' prompt to get full invulnerability:

 GodDebugToggle()

 This code thats was public first:

 mdkGobSetDamageFilter(mdkGetPlayerGob(),0)

 Looks like the programming language? Yeah - this is trick for
 internal game scripting system. But please note what this code must
 be re-entered periodically because game doesn't store previous mode
 while map block change (block changing can be determined if your
 HDD reads something heavy and game is slowdowns for a while, or just
 see what you now is not invulnerable and your health value is
 decreasing). Hopefully you can not to re-enter this long code - you
 can just bring console ('~' key) and then press Up-arrow key to get
 previous command form history.

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 The level cheats also have to be entered at the prompt:

 mdkNewGame(1,12)     Warp to Level 1
 mdkNewGame(2,12)     Warp to Level 2
 mdkNewGame(3,12)     Warp to Level 3
 mdkNewGame(4,12)     Warp to Level 4
 mdkNewGame(5,11)     Warp to Level 5
 mdkNewGame(6,8)      Warp to Level 6
 mdkNewGame(7,11)     Warp to Level 7
 mdkNewGame(8,8)      Warp to Level 8
 mdkNewGame(9,13)     Warp to Level 9
 mdkNewGame(10,7)     Warp to Level 10 (Final)
 mdkNewGame(11,1)     Warp to Level 10 #1 (Special)
 mdkNewGame(12,1)     Warp to Level 10 #2 (Special)

 Submitted by Cyberman, cyberman@ag.ru

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 Type KurtGetNaked() in the console and then mdkNewGame(1,12) then Kurt
 will be naked when you play level 1. This works for any level that Kurt
 plays in. Just type KurtGetNaked() and start the level with Kurt in it.