There may be but one hope for the existence of the Eldar race and this hope lies in one the Eldar call Ynnead. But just who or what is this God of the Dead?
Via our good friends at Lexicanum
Ynnead represents the last hope of the dwindling Eldar race. They believe that when the Infinity Circuits hold all the spirits of their race, all of the Craftworlds will unite into one Infinity Circuit, and the collective spirits of the Eldar will join to form a new Power in the Warp that will battle and subdue Slaanesh, so that Eldar spirits may once more be able to merge with it and form a single, balanced entity.
By doing so, if such a thing is possible, they hope that this will allow the Eldar race to be reborn into a better form. Meanwhile the Craftworlds and the spirit stones must be guarded from harm and continue to survive, so that all Eldar can see and form in their own minds a concept of the Eldar virtues that will enter along with their spirits into the Infinity Circuits.
Ynnead itself (the God of the Dead) is supposedly a nascent Eldar god growing in the collective Infinity Circuits of every craftworld, from the souls of dead Eldar. It has yet to manifest itself, as it has yet to attain enough power to fulfill its purpose: to destroy Slaanesh and free the Eldar. Its relationship to Kaela Mensha Khaine is unclear.
As Eldar die and their souls become part of the Infinity Circuits, the god grows in power. A few Eldar Seers believe that once every single Eldar has died, Ynnead will awaken and have the strength to defeat Slaanesh forever. In 991.M41, the Eldar Mystic Kysaduras proclaimed that the only hope of Eldar survival in the End Times would lay with Ynnead.
Eldrad Ulthran attempted to undertake a great ritual that would prematurely awaken Ynnead, involving channeling the remains of Farseers through every Infinity Circuit. The ritual would have rendered every Craftworld disabled and wreaked havoc on the Astronomican, but Slaanesh may have ultimately met its end. However he was foiled by the Deathwatch in the Battle of Port Demesnus.
The Astronomicon? So what if it’s the Emperor that is destined to receive the power of the farseers, and become reborn as Ynnead? I mean he does eat the souls of mere human psykers on the daily, what do you think the souls of every potent psyker from the Eldar race do for the God-Emperor’s diet?