Summoned Old God

The Summoned Old God was an Old God that was being summoned by the Dark Conclave to Outland. The summoning ritual was interrupted by an adventurer and the ritualists massacred. This Old God is not related to the ones trapped on Azeroth.

Background
During the rise of the Orcish Horde, the arakkoa turned away from the veneration of their gods Rukhmar, Anzu, and Sethe. Without champions to defend the arakkoa the Sethekk cult gained more power in arakkoa society, spiraling the race into darkness. The arakkoa came to worship this Old God as their new master, who promised them untold power and status in the cosmos. The Sethekk believed themselves to be the true and most loyal followers of this being. However, they incorrectly interpreted the destruction of Auchindoun to be the arrival of their master on Draenor.

Later, while the Horde massed under Gul'dan, the arakkoa sought to defend themselves from the threat by striking against him. Gul'dan learned of their intentions and cast a mighty spell that destroyed their camps and twisted their spirits.

On Outland, the spirits of the Dark Conclave sought to summon this ancient and powerful evil through a ritual conducted at the lava pits to the south of the Sketh'lon Base Camp. Gul'dan's magic mingled with their own, empowering them to aid this creature in manifesting in Outland. Had they been successful, the death and destruction it would have brought would've been unimaginable.

Objective of

 * Thwart the Dark Conclave

Trivia

 * The Summoned Old God uses the same model as the Old God C'Thun.

Speculation
The Black Blood of Draenor may be related to it, similar to Yogg-Saron and the Black Blood of Yogg-Saron, or the oozes associated with the corruption of Vordrassil. Oozes, in general, may be related to the Old Gods.