The Rending of Palaghast
The overall term for the Demons and Devils created by the Being From Beyond.
They roam the Abyssal Sea looking for weak points in the power of the Solars that keep them at bay. Only with the aide of the noble races, often cults and worshipers, can they enter a Domain. These are often summoning circles and portals.
Rumor has it that they still have a sizable host that surrounds the Heart of Palaghast, looking for a way into the sphere where they can destroy it once and for all.