Great Old Ones

Far beyond the edges of this universe lies a predatory, alien, far realm. The evils of that place leak into our reality from time to time in the form of aberrations. The Great Old Ones of that realm constantly hunger to feed on our world, and will occasionally make pacts with mortals to to their bidding from afar.
When the Sister-Moons called out for gods to come to Ancathra, they also inadvertantly called out to the Far Realms. Having alerted the ancient evils to Ancathra's existence, several of them began to slowly turn towatds this mortal world. Nishoggua the Night Serpent heard the call first, and moved quickly to enter this new plane. Soon after, the Great Old One Shathoggua the Repenter feared that contact with Ancathra would pollute the Far Realms and dilute their power. Forming a pact with the Sister Moons, Shathoggua helps prevent any of the Old Ones from physically entering this world, fearing they would return tainted.