Eidola are Rithera's "outsiders," its equivalent to demons or devils, a rarely encountered but dire foe of humanity and beastkin alike. They are accidental fusions of elemental and domain-aspected aether, a twisted version of life that originated unintentionally during the Primordial Wars, when the Gods of Creation and Destruction fought each other with massive amounts of their respective aether. This help file discusses eidola's powers and limitations.
For reasons that will be explained, eidola mostly cluster around the three Gates, and because the Gates of Creation and Purification are very isolated, encounters between humans and eidola largely take place in Eurena on the eastern continent, near the Gate of Destruction. (The paladins of Revonus's vow to destroy eidola is attributable in part to this proximity.) To those outside of Eurena, eidola are generally considered to be merely a frightening fable for children. Thus, this information is largely OOC.
Though eidola vary widely in their appearance and capabilities, all of them share one trait: they continuously emit a "distortion field" that is harmful to mortals, who quickly become disoriented in the mere presence of eidola. After extended exposure, humans and beastkin seem to go mad, either acting incoherently or becoming inert. Because of this terrifying constant and their typical aggression, eidola are assumed to be evil. In reality, most are simply alien, acting on hunger and an almost randomized set of goals. Only a minority are intelligent, and many of those "sapient" eidola are indifferent to mortals or even benevolent. Those that are cruel are, however, truly formidable adversaries.
What prevents eidola from overtaking the world is their insatiable need for whatever domain-aspected aether happens to define them. Because most naturally-occurring wellsprings of aether are elemental (fire, water, wind, or earth), eidola tend to cluster around the Gates to feed and avoid wasting away. The primary source of domain-aspected aether other than the Gates is, of course, souls, which explains why unintelligent eidola are consistently aggressive toward mortals. However, note that all eidola by definition have both a physical "body" (material or elemental aether) and a "soul" (domain-aspected aether), and so are not ghost-like and are not capable of the "possession" of living or dead bodies, contrary to some fearful rumors.
In their base form, eidola appear like dark storm clouds, a black fog laced with electrical nodes. However, by the time most eidola are observed, they have taken on an appearance associated with their domain and with their environs. Because of their hunger for and sensitivity to aether associated with the soul, some eidola appear to be shaped by a collective unconscious, eerily taking on aesthetic traits reflecting nearby human societies. If lower-ranked eidola could travel, their appearance would likely change with their environs, but because of their high energy consumption, it is thought that only higher-ranked eidola (which already have more defined forms) are capable of such mobility.
The four "classes" of eidola are defined by Cosmopolitan scholars as follows:
* REMNANT: Remnant eidola are the lowest form, only technically eidola, the fusion of a fragment of soul and some material by divine-level power. Humans and beastkin slain during the Primordial Wars became remnants when struck by the gods, their souls shattering and pieces affixing to the earth, giving rise to strange phenomena like "clips" of memories that play like a movie on loop for passerby. Remnants are likely not sentient. They are unable to move, react to, or act on their environment, and are sometimes mistaken for hauntings or mirages. Their innate distortion effect is limited and highly localized, but passing through a cluster of them can be dangerous.
* ENIGMA: The standard class of eidola, a more complete fusion capable of movement and aggression that acts by its own strange logic. Though all eidola enigma-class or higher hunger for domain-aspected aether, an enigma is so named because each one has its own bizarre and unintelligible patterns of behavior. It is hypothesized that this is because an eidola's "soul" is incomplete, a kind of contextless chunk of divine intention, and the eidola translates this into acts or habits that seem to make no sense and relate to no purpose. Combined with its violent nature and more dangerous distortion effect, this renders the enigma-class eidola a terrifying enemy.
* MARAUDER: A large eidola with a distortion effect so powerful that it can "corrupt" other enigma-class eidola into lesser versions of itself and thus tends to move as the "leader" of a pack. Being large, it is more desperate for aether and so more aggressive, sometimes seeking out communities of sentient beings. Unlike lower-ranked eidola, it is capable of preserving itself by "hibernating" away from a Gate until it senses aether with which it might sate its hunger. Thus, any eidola encountered far from the Gates is likely to be a marauder-class eidola and/or its minions, with the fearful potential to appear seemingly out of nowhere as it bursts from its lair. Like lower-ranked eidola, however, it remains alien and incapable of being reasoned with.
* SAPIENT: Intelligent eidola capable of communicating with mortals. Those hostile to humanity are some of the most dangerous enemies to exist, exceedingly powerful and terribly cunning. Those that are benevolent must take care in how they approach humanity because of the sheer power of their innate distortion effect.
There remain three secrets of the eidola known almost exclusively to the Loremasters: 1) the means by which the distortion effect of eidola may be contained or inhibited, 2) the nature of the so-called "eidola-pacted" and "eidola-touched," and 3) the true nature of the eidola's distortion effect.
Sapient eidola have devised various ways of coexisting with mortals, either to assist or to manipulate them. The simplest is through ritual magic, constructing a shrine or temple with sanctified boundaries, though this prevents the eidola from traveling. (Such eidola end up being known as spirits or demigods.) A more complex method involves feeding off of the "emanations" of mortal souls, like thoughts or dreams, until the eidola resembles a mortal themselves and becomes capable of self-suppression. (Some suspect this method is merely a myth, but the clergy of Revonus are die-hard believers in such eidola, calling them "Infiltrators" and often premising inquisitions on their supposed presence.) But there is one more method: an eidola, much like a soul, may be contained or stored inside of the fragment of a star, "dematerializing" into pure energy without being destroyed. This is the only context in which an eidola may, in being deconstructed, seem to take on a spiritual form and "possess" an object. Though few know of this fact, the Magitech Cannon of Cosmopolis was powered by a trapped eidola in just such a way.
Fewer still know of the mortals who have become one with eidola. The "eidola-pacted" are those individuals who have fused physically and spiritually with an eidola, becoming a single entity. Mortals may attempt to fuse with eidola out of instinctive desperation at the brink of death, madness, or occult knowledge and terrible ambition; sapient eidola may choose to do so for similar reasons, and lesser eidola may do so for their own enigmatic ends. When this occurs, instead of the eidola devouring and digesting the mortal's soul, both body and mind meet in the middle between the beings, transforming irreparably, most commonly through the appearance of tattoo-like markings and a jumbled sense of self to which is added strange and intense drives. The eidola-pacted no longer emit a distortion field, allowing them to blend in with society if they hide their strange physical changes. But it is thought that a sapient eidola and a skilled mage protected with the proper rituals could fuse instead into a self-suppressing eidola, still capable of unleashing that distortion field and empowering themselves at will.
Though the eidola-pacted are rare to the point of being nearly unknown, the "eidola-touched" are lesser known still: descendents either of the eidola-pacted or of a coupling between a mortal and a self-suppressing eidola that came to resemble a mortal. Any eidola-touched is almost guaranteed to be born a powerful and talented sorceror.
Finally, though it is only hypothesized, there is an answer to the mystery of how the mere presence of the eidola maddens mortals: they distort one's subjective experience of time. The Goddess of Purification is associated with time as the necessary medium of progress. The eidola are, in a word, "anti-Purification": they are an intrinsically entropic force that emerged from the war that sundered the world and threatened to return form to chaos.
Think of how time flies when you are having fun or seems to slow when you are bored. Now, imagine having such experiences without knowing why. Without a reasonable context -- like "Ah, I was having fun then" or "I was bored" -- feeling out of step with the passage of time is highly discombobulating, leading to frequent confused hesitation even in dangerous circumstances. Extended exposure has a more radical distorting effect on one's sense of the temporal order. Those driven mad by eidola can no longer tell that their memories belong in the past and their aspirations aim toward the future. It becomes impossible to know how to act, on the basis of what or to what end. Thus, those deeply affected by this corruption either act senselessly or not at all and, unless cared for by others, inevitably meet a tragic end.