Cheat:
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 After playing Myth III through fairly good, I discovered 
 that old cheat codes still work in this game. So, if 
 you want to get access to all maps then holding Shift 
 button down, click on "New Game". If you want to win 
 the mission then you can hold down simultaneously three 
 buttons - Ctrl+Alt "+" on the NumPad, but if you want to 
 lose the mission then you should do all the same but 
 Numpad "-".