PDZ video walkthroughs, on Dark Agent

If you're having some trouble making your way through Perfect Dark Zero, then watching these walkthrough videos completed on Dark Agent difficulty will either:

• Help you immensely, giving you that little edge you needed to make it through a tricky part...
• ...or crush your gaming spirit, quickly and wholly, reminding you that no matter how good you think you may be, there are an infinite number of people all over the world who are infinitely better at video games than you are.
  

Dark Agent can only be unlocked after completing the entire game on Perfect Agent. Cheat Code Central has this to say about Dark Agent mode: "You don't even want to know about the Dark Agent. Only the hardest of the hardcore will see the ending credits on this difficulty level."
[Thanks for the tip, Efrain]