Machin Shin

Machin Shin is an entity that resides in The Ways, whose name in the Old Tongue means the Black Wind. If ever it comes into contact with a living being, it consumes the victim's soul and often their body. Any who lose their soul to such an encounter but survive are driven insane or suffer a waking death.
The exact nature of Machin Shin is unknown, as are its origins. It's scope is unclear; though it is not omnipresent, it is "vast as The Ways," and can manifest itself in many locations at once. It is unclear what degree of sentience Machin Shin possesses.
Machin Shin appears to be some sort of semi-sentient entity made up of darkness that flows like air. Survivors of encounters with Machin Shin tell of feeling a light breeze in the Ways preceding its arrival, easily noticed as there is normally no wind in the Ways. They also speak of hearing thousands of screaming voices, which might manifest as rambling monologue obsessed with blood, screams, violence and terror. Some seem to hear the screams separately from the monologue. Padan Fain is the only being yet that was released by the wind after it was caught and Fain speaks about some voices greeting and some even fearing him. It also can identify people, as when Rand first encountered it zeroed in on Rand's blue-gray eyes and the monologue began including begging or threatening to take his eyes for its own.
Exactly what occurs when Machin Shin fully envelopes someone is not known, except for some of its effects, insanity or a waking death.