Voidtinged Substance

Voidtinged Substance drop from the following mobs in Nazjatar:
 * Lesser Zoatroid
 * Shirakess Voidtwister
 * Deepcoil Serpent
 * Shirakess Apprentice
 * Shirakess Voidreaver
 * Zoatroid
 * Deepcoil Constrictor
 * Elder Mindbreaker
 * Gler'thogg

As a quest objective

 * Deepcoil Cleansing