Myrddraal (thing)

A few more additions:

• They do indeed have hair, and I think what Jordan was getting at when he described it as oily is that it hangs close to the body; it doesn't have body or luster (they don't use Pantene). However, there is one woman than could attest to the fact that Myrddraal do or don't have hair down there: Moghedien. She was raped by Shaidar Haran, and although he is far from a typical Myrddraal, he is similar in many aspects, and it is doubful that the differences include physical things (other than his height). This is only hinted at in the books, but was confirmed by Jordan, and is in the infamous FAQ.
• A wound from a Myrddraal blade usualy kills fairly quickly, though nothing at all like Padan Fain's Adriol dagger (or Shadar Logoth, if you will). The reason that they are so deadly is the fact that the forgers at Thakan'dar temper the blade in the foul waters of the river, and then plunge the blade into a human, somehow trapping a portion of the soul, or something to that effect.
• To turn someone to the Shadow requires thirteen Aes Sedai (usually Black Ajah), and thirteen Myrddraal. The reason that it's thirteen is probably the fact that the largest circle that can be achieved by women without a man is thirteen. That and the fact that thirteen is traditionaly an unlucky number, so it probably seemed appropriate to Jordan. There may (and are probably) other undisclosed reasons, as the topic hasn't really been delved into much.
• In the typical chain of command for forces of the Shadow, Myrddraal are second to last. In the past, orders have always been carried out through the chain:

  Dark One --> Forsaken --> Dreadlords --> Myrddraal --> Trollocs

  It should be noted that the Dark One isn't always included, as the Forsaken are always scheming, and Darkfriends of high standing may be incorporated into the chain, but as this is an Army of Evil (TM) fear is often the motivating factor in obedience. Each member of the chain effectively scares the party below it into follwoing orders, as seen when a Forsaken had to force the Myrddraal to force the Trollocs to follow Rand and Co. into Shadar Logoth, and later, the Aiel Waste (Three Fold Land).