Eidolon

Supernatural creatures formed from the memories and collective grief, fear and suffering of humanity stemming from the Vanishing. They each have unique superpowers like metahumans and they are believed to be either representative of vanished metahumans or some corrupted apparition of them caused by their manner of death.
They dissipate if they take enough physical damage, though this isn't always as easy to accomplish as just hitting them hard enough with the variability of power sets they can form with. In general, they have hard exteriors that weak enough calibers of bullets can't penetrate, even before adding extra powers to the mix.
Because they appear in places that are experiencing high amounts of pain and suffering, places like prisons, funeral houses, graveyards, memorial sites, and battlefields see eidolons form in them the most often. This leads to prisons being simultaneously extremely heavily patrolled as well as prisoner conditions being much nicer and more humane in many countries compared to what they used to be before the Vanishing. Some more corrupt countries actually patrol and guard them less and instead leave the prisoners at the mercy of eidolons which they clean up later on.
Dedicated funeral homes and cemeteries have also become things of the past in most places since having specific places where people gather to grieve increasing the rate of eidolon creation too much. Instead, funeral homes are mobile affairs that move from place to place every few days and cremation is required by law in most places barring extenuating circumstances where a traditional burial will be permitted.
Existing cemeteries (and memorial sites) were left alone out of respect for the dead but as a result a not-insignificant amount of Icarus manpower goes towards patrolling and guarding cemeteries around the world, while interred ashes were in fact relocated to their families.
A memorial site for the Vanishing was made in the years as Icarus compiled a list of the vanished metahumans but because it was a worldwide event, they created this memorial site in cyberspace instead of physically and although they tried to forbid governments around the world from building their own physical memorials, many defied Icarus since they'd lost most of their power and as a result created eidolon epidemics within their borders than either Icarus would have to clean up later or which they themselves would lose many resources and lives to, leading to them taking their own memorials down later.

Basic Information

Anatomy

They vary in shapes and sizes as much as their powers do, but their bodies always appear to be made of an oily and shadowy black substance. They don't have skeletons and instead are entirely made up of this substance which is usually solid, with the consistency and hardness of muscle, but when separated from the body through injury, it evaporates, leaving no trace behind.
They usually come with at least four glowing yellow orbs for eyes but can have any number of them.

Genetics and Reproduction

They can't reproduce with each other. Instead, an eidolon forms out of thin air, sporadically and in seemingly random locations. Their formation has been traced and linked to a large radius where high amounts of grief and melancholy is being experienced at once. Because the Vanishing was the inciting incident, this usually makes it hard to predict where exactly one will unless there's specifically been a separate mass death event or a funeral.

Ecology and Habitats

At a base level, they can appear and exist in nearly any environment, including extremely hot and cold temperatures that humans can't survive in without assistance. However, the random nature of their abilities and attributes means that a Fury can appear somewhere it can't last long in, leading to it either escaping the environment or dying and dissipating.

Dietary Needs and Habits

They don't require food to exist and their presence is supported by the mass of negative feelings that spawned it, something that can only be tracked by a very specific set of metahuman abilities. If all the negative emotions that created it disappear, so does the eidolon but there has only been one verified account of this happening.
They roam around, driven by an instinct to kill humans and feed on their unfulfilled lifespans at the moment of death.

Behaviour

Non-psychic eidolons can sometimes be distracted with empathy and being treated like people since it reminds their past lives, but this doesn't last long and is only done by Icarus agents as a tactic to slow down an eidolon's destructive spree and stall for time for civilians to clear an area or backup to arrive. Even then, this can sometimes backfire or fail altogether because of the particulars of the eidolon's past life which anyone non-psychic wouldn't be able to even begin to discern anything about.
Psychic eidolons, on the other hand, display complex behaviour, usually malicious in some form since they're still driven by a base desire to fill the void inside them with pure life. They're more likely to either go out in search of loved ones or other people specific to their memories, or people who remind them of such.

Additional Information

Domestication

Eidolons cannot be domesticated. Many attempts have been made to do so with less powerful ones but they have all been unsuccessful.

Average Intelligence

Normally their intelligence is around the level of a wild lion or wolf. However, eidolons that form with psychic abilities can approach human-levels of sapience and intelligence, making them the most dangerous kind to encounter.
In these cases, they might even share some memories with the metahuman they are based on, usually in some kind of corrupted and stunted form.

Perception and Sensory Capabilities

Their senses are usually 1.5x more acute than a human's but this can vary depending on the metahuman abilities they have.

Civilization and Culture

History

Furies first appeared in the wake of . It's been theorized that N-Day caused the creation of Furies which has persisted through to the present day and even remained after The Wiltingwell Incident.
By now, humanity has been dealing with Furies for 61 years.