See  [67-68] Void Terror for the specific mob.

A void terror is a huge and extremely powerful two-headed demon. This beast possess a nearly unlimited source of demonic energy. The only known void terrors residing in Azeroth are Immol'thar found within Dire Maul in Kalimdor and Occu'thar found in the Baradin Hold raid in the Eastern Kingdoms. A large number of them have been sighted in Outland, guarding certain regions of the Blade's Edge Mountains and prowling the Netherstorm.

Named void terrorsEdit

•  [61+] Immol'thar
•  [70+] Yor <Void Hound of Shaffar>
•  [??] Occu'thar