Demonic Rune

Source
This item is a drop from high-level demons. The best places to look are the demon camps in Felwood, Azshara and in the eastern part of Dire Maul. They can also be found on the elite demons in Winterspring and Blasted Lands.

Blacksmithing

 * Corruption (sword)
 * Demon Forged Breastplate

Tailoring

 * Felcloth Gloves
 * Felcloth Robe
 * Felcloth Shoulders
 * Robe of the Void

Jewelcrafting

 * Ring of Bitter Shadows