A dark, viscous liquid, it appears as if a complete void of blackness. It is pure corruption, and drinking it can have terrible, corruptive effects on the person consuming it.
In SY06. Tomb of Dying Dreams, Part II, powerful and ancient entities, Xanatha, Fangafa, Queen of Thorns, and the Creeping Darkness all wanted it's power; in the end, the Creeping Darkness was the victor