The developers of Counter-Strike: Condition Zero: Deleted Scenes at Ritual Entertainment (who worked on the game from August 2002 to June 2003) left in the game a secret hidden difficulty, known simply as "skill 0". It was compared by a developer, Reid "BrushBaron" Kimball', to the Nightmare mode from DOOM. He also referred to it as "Nuckin' Futs".

This is the highest difficulty in the game, and which the developers considered to be a true Counter-Strike-like experience which replicated the intensity and difficulty of real online CS play.

When Deleted Scenes was finally launched with Condition Zero in Nightmare difficulty is not available from any in-game menu, however it can be accessed by:

• opening the developer console using the tilde (~) key to the left of your "1" key
  
• and typing the expression "skill 0" without the quotation marks into the console.

You must do this just after you have loaded into a map, since the game forces you to choose between Easy, Medium and Hard from the World Map. You can check that Nightmare is enabled simply by typing "skill" in the console, and the game should reply back with the expression: skill is "0"

Once you activate "skill 0", it is added to the internal player configuration file and persists through all save games, game restarts and maploads. So if you finish a mission, Nightmare mode will still be active in the next one.

The Nightmare difficulty results in higher damage from enemies. This means more damage will go through your armor, and that your armor will be more quickly destroyed by incoming damage - so you will need to conserve your health and your armor vest much more than before.

In addition, enemies appear to react more quickly and are more aggressive. Even the first mission, Recoil, is now extremely difficult right from the beginning. 3 terrorists can bring you down to 0 HP in the first area.

In the humble opinion of the author, this difficulty mode is the true way to play Deleted Scenes as the game is now actually challenging, and strategy, resource management and tactics become much more meaningful - and feels as difficult as the actual Counter-Strike game.

• Reid "BrushBaron" Kimball's reply to a thread on the Ritualistic community forums: http://www.ritualistic.com/forums/showthread.php?t=11629
  
• Thanks to the CS Wiki and the contributors' research for first discovering the original post.
  
• The thumbnail picture for this guide comes from the Ritualistic screenshot gallery for Condition Zero.