From Tar Valon Library
Machin Shin, or the Black Wind is a thing of The Ways, that will steal the soul of anyone who encounters it that is unable to defend themselves, although Padan Fain claimed to have understood it and that it left him alone (TEotW, Ch. 47). When it is close to a person, it takes the form of many voices, crying out (TGH, Ch. 33). It is not known where it came from, though there are many suggestions, such as a natural parasite, something created by the decay or a remnant of the Age of Legends (TWoRJTWoT, Ch. 22, TEotW, Ch. 45). It is believed that it cannot be controlled, however it was found to be waiting at a Waygate to prevent Rand entering the Ways (TGH, Ch. 33), where it seemed to try and come out, and then again at a nearby Waygate outside Stedding Tsofu (TGH, Ch. 36). It is attracted to people traveling the Ways, the more people, the greater the chance of it finding them (TSR, Ch. 44).
It catches Padan Fain, but does not consume his soul instead fleeing him (TEotW, Ch. 47).
"Something left from the Time of Madness, perhaps, or even from the War of the Shadow, the War of Power. Something hiding in the Ways so long it can no longer get out. No one, not even among the Ogier, knows how far the Ways run, or how deep. It could even be something of the Ways themselves. As Loial said, the Ways are living things, and all living things have parasites. Perhaps even a creature of the corruption itself, something born of the decay. Something that hates life and light (Moiraine, The Eye of the World, Chapter 44)
"Blood so sweet, so sweet to drink the blood, the blood that drips, drips, drops so red; pretty eyes, fine eyes, I have no eyes, pluck the eyes from out of your head; grind your bones, split your bones inside your flesh, suck your marrow while you scream; scream, scream, singing screams, sing your screams..." (To Rand, The Great Hunt, Chapter 33)