Press the tilde key during gameplay to drop the console and enter the following codes:

• Loaded - All ammo and most secondary weapons.
  
• Ghost - Walk through walls
  
• PlayersOnly - Freezes everything
  
• AllAmmo - 999 ammo
  
• Fly - Allows you to fly.
  
• God - Makes you Invincible
  
• Slomo X - where X is how fast the game will run
  
• thematulaaklives for god mode
  
• fierfek for ammo restoration
  
• darman to skip a level