Screamer

Like Discs and Flamers, Screamers are beings of pure energy in the Realm of Chaos. They flit about on the currents of magic, fighting with Discs for the souls of the dead. But when a host gathers, the Screamers are drawn by extremes of emotion, often brought on by the tensions that mount before a conflict. They slip free from their Aethyreal bonds to enter the world of Men and circle overhead, sampling the flavours of Human emotions. The Screamers follow armies into war, sensing a great harvest of souls to feast upon. And during brutal conflicts, they dive from the heavens, issuing their horrific scream as they rip through the ranks of enemy soldiers, slicing through armour and flesh with their horned and toothed bodies before lifting up once more to ride the currents of the Winds of Magic.

A Screamer is a large glimmering being that looks something like a mutated purple manta ray. All along the edges of their flattened bodies are sharp barbs and horns. Their tails extend out behind them for a few feet, ending in a horned, mace-like tail. They can be easily spotted by the streaks of colours they leave wherever they fly.

These things are not intelligent beings; they survive by instinct alone. They are drawn to extreme emotion, drifting towards places where agony, love, and hate run fierce. Once they discover such a rich place, they tease out the souls to feast upon as they depart for whatever reward they hope to attain.

Source

 * Warhammer Fantasy RPG 2nd ED -- Tome of Corruption (pg. 232)