"They are an impersonal force of the universe, creativity, which assumes an individual role only in response to the creative impulses of mortals – our art gives it form, our writing gives it name, our music give it a voice. It is no more of an immortal than gravity is, no matter how many people worship and ascribe it a personality and an intelligence."
– Last Independent Words of the Wizard Slaader
For unknown aeons, beyond the farthest reaches of mortal knowledge, far from the influence of any known immortal, within the realm merely called The Beyond by mortal scholars; there exists a great writhing plain. Black stars in a bright sky ever illuminate the plain, which to a casual observer may appear as naught but a great murky, turbid sea; to those who may dare to gaze closer however, the expanse is composed of alien "invertebrates" without number. We say "invertebrates" because that is what they most closely resemble within the mortal realm; some may seem as innocuous as a common worm, ant, or beetle - others form strange and alien forms that would seem to have no way of existing, yet move and act as alive as any other. Ever has the writhing plain existed, largely as it has, undisturbed and unchanged - until the arrival of "The Wizards".
During the time known to mortals as the "Age of Wonders", the mortal wizards, seeking to map and understand the known realms in pursuit of ever greater knowledge, reached The Beyond; but in doing so they cut themselves off. Unable to return, they set their powers to survival and necessity, crafting a grand structure to shield them from the rigors and denizens of The Beyond. Upon waking they found that several small, crude structures had been erected within the writhing plain. Thus did they give rise to the first, and only, Civilization in The Beyond.
Over unknown time, as the "days" on the writhing plain are not as they are in the mortal realm, the Swarm and the Wizards did observe each other. The Swarm took well to the creation of things, though they always possessed an air of surrealism manifested as the epitome of the object; a table would appear as a table, a perfect table, an eternally perfect table - the existence of which violated the mortal notion of entropy and deterioration. Purposefully trying to harm or destroy the objects created by the Swarm was a fruitless endeavor as well, as the object in question would repair itself rapidly - even upon the complete and utter destruction of an object through the use of magic, the object would appear again, intact and whole, sometime later, seeming to have simply reappeared, though not always in the location of its seemed destruction.
The Swarm did not communicate through any audible means, but rather they could exchange ideas through some form of telepathy. The Wizard Slaader took particular interest in the Swarm, while the others turned their pursuits to studying other phenomena and aspects of The Beyond. As he spent more time with the Swarm, they eventually took on the vaguely humanoid shapes which mortals now call "Mass of Maggots". They began grander constructions, and undertook writings; thriving on creation. In exchange for the knowledge of the Wizard, the Swarm granted knowledge they had of aeons past. This knowledge allowed the Wizards to attain even greater powers within The Beyond, though they had no inkling of the toll such knowledge would take.
The eldritch knowledge imparted by the Swarm began to fester within the minds of the Wizards, rotting away at them from the inside; stripping them of their humanity and sanity. Too late did they realize what was happening, and when they did the Swarm were aware of their horror and desperation to return to the mortal realm. The Wizard Slaader, who first took interest in the Swarm, sacrificed himself so that the others may escape a similar fate; becoming part of the Swarm. Upon their return to the mortal plane, the Watchers, as they are now called, did perform one grand act in the form of a geas to attempt to protect against the Swarm. Several phenomena are a direct result of this geas, though none may suspect it: déjà vu and earworms are both effects of the geas to protect the mortal mind from exposure to the creations of the Swarm.
Now deprived of the source of their creative thoughts, the Swarm now seek ever to find more mortals. The mortal realm is anathema to the Swarm, they cannot long survive without a suitable host or connection to The Beyond. Where possible they will seek out hosts who are most creative: artists, writers, musicians, scholars, mages - forming a symbiotic relationship. At first this relationship is mutualistic, the Swarm survives, and the mortal will often become known as one of the great minds of their generation, excelling in their particular field of creativity. Eventually though the relationship always becomes parasitic, the otherworldly knowledge and insight granted by the Swarm eats away at the humanity and sanity of the host, until they either lapse into complete madness, or actually die - their mind shattered under the weight of cosmic intellect.
In lieu of a host, an object may sometimes serve as a connection to The Beyond. This object will always appear as a perfect example of what it is, though closer or prolonged inspection of it will reveal the surreal qualities outlined above. A painting in the house of a lord may never fade or chip, and never need dusting or cleaning. More complex objects may appear upon first viewing to be normal, but will perform their function without necessary components; a clock may keep time, but upon opening it there are no gears or constructions inside - it is the perfect epitome of a clock on form and function from the exterior.
Without host or connection to The Beyond, the Swarm will form a "Mass of Maggots" to prolong their survival; feeding off whatever residual connection to The Beyond they possess, slowly becoming naught but regular invertebrates or decomposing into blackened dirt if their form is too alien to adapt to the constraints of the mortal realm.
The Swarm exist as a hive mind collective, so they all know and perceive what any know or perceive. The only exception is a disconnected group, trapped on the mortal realm, which forms a "Mass of Maggots" out of survival; without any connection to The Beyond they form a much weaker connection amongst themselves to try and survive. The Swarm does not recognize individualism, they believe that the "Wizards" are simply part of the "mortals" just as an individual invertebrate may be part of the Swarm.