Outsiders

"They are insanely violent, insanely powerful, and just plain insane."

— Harry Dresden

Outsiders is a colloquial term referring to all the beings hailing from Outside the Brass realms. They do not occur naturally on Haven, though they can be deliberately summoned by their mortal followers or arrive on rare occasions on shooting stars. There have also been several large scale-incursions in the past, the remnants of which still linger.

They are anathema to the very structure of the brass realms, not conforming to its rules and either deliberately or inadvertently bring destructive change to the realms. They are in most cases worse than even the most vile demon native to the brass realms, for while Angels and Demons fight endlessly over the souls of mortals in a grand game, outsiders would end the game entirely by putting an end to the Brass Realms as they are.

Description

Aura of unease: Just as the order of the Brass realms is unbearable to them, they are unbearable to creatures of the Realms. Any being of the realms can identify outsiders as not belonging. They emit an aura of tangible unease, they simply feel wrong, as if they shouldn't be. Most creatures of the Brass Realms react to this aura with either aggression or fear.

The oblivion War: The outsiders are opposed in their pursuit of changing the order by the Mechanoids. The Mechanoids regularly sweep the brass realms for traces of outsiders, and if they spot a sufficient breach, take action. Their methods however are devastating and in many ways worse than the outsiders', for they care not about what might be caught in the crossfire of their cleansing.

Rulebreakers: Similarly to Fellstone, outsiders are not fully beholden to the laws of the brass realms and are thus able to do things that should be impossible by the laws of physics, so long as they are powerful enough or enough of them congregate in one area. They can do things like time travel, negate entropy, kill immortals and other nonsensical things. Luckily enough they have trouble doing this reliably and can be opposed.

There are many different kinds of Outsiders, belonging to seemingly different factions. While some of them are definitively malicious, some are ambivalent or even well-intentioned, though they are all universally disruptive and not taken lightly.

Types of Outsiders

Dissolvers

A Dissolver is an amorphous liquid more than a functional creature. They are neither fast nor smart, the main danger they present is that they instantly liquify anything they touch- be it rock, steel or living flesh.
They and their affected area are likely to look like a big lake of mud or a very flat stone, the presence of the dissolver unnoticable unless it is actively expanding. They are impervious to physical damage as a result of their physiology, but can be killed by fast temperature changes or various chemicals.

Foulspawn

Foulspawn are twisted, warlike invaders. They are not subtle, invading the realms through ceaseless agrression and brute force, with no sense of self-preservation. They are a babbling, screeching horde of seemingly randomly assembled creatures bound by the shared wish to destroy the Brass Realms utterly.
They corrupt reality wherever they go, with the ultimate goal of causing sufficient disruption that they rip entire realms out of alignment and throw them into the uncaring void. Any incursions need to be dealt with swiftly before they grow out of control.

Glimpse

A Glimpse is a curious creature; none can clearly say what it looks like, for it does not exist while it is being observed. If anybody is looking at the creature, it immediately disappears, reappearing in the same spot once nobody is looking. This process is automatic and instantaneous, and extends even to severed body-parts and persists upon death.
Beyond that, a Glimpse is a predatory organism that preys on animals and humans as able. It is stealthy but it does produce sound, and its preferred hunting method is to sneak up on prey, wound it and then pursue it while continually wounding it until it dies either of blood-loss or exhaustion.
So long as nobody is looking at the creature, it is there, and while that means that it can hurt others, it can also be hurt. If one uses their eyes to create distance and closes them at the moment of attack, the creature is manageable.

Gray Haze

The Gray Haze is a supernatural affliction akin to a disease, spread by skin-to-skin contact and close proximity. It rapidly dissolves the flesh of the afflicted, leaving only bones behind. It is visible as a gray mist or haze on the affected area and spreads rapidly to the rest of the body as the victim is consumed. Any physical contact is sure to spread the haze and any contamination is certain to be lethal within days if left untreated.
The Gray Haze is actually a swarm of microscopic carnivorous insects, akin to locusts. They rapidly reproduce and devour any creature they land upon, and can remain alive on a deceased victim's bones for days or even weeks afterwards.
However, the insects cannot breathe underwater and rapidly drown if submerged.

Mirrorlings

Mirrorlings are among the most dangerous outsiders, able to threaten entire regions or even entire worlds by themselves.
Mirrorlings cannot be defeated in combat. If a mirrorling dies, it instead splits into two identical copies. One becomes two, become four, become eight, become sixteen, become thirty-two, become sixty-four and so on.
The only thing that can kill a Mirrorling without creating more of them is another Mirrorling, until only one is left, which they will do if there are no other targets nearby.
Mirrorlings instead must be contained and imprisoned or they will eventually overcome all adversity.

Moodlights

Moodlights are among the most harmless of outsiders. They appear as incorporeal spheres of coloured light. They drift slowly, unaffected by wind or weather, hovering slightly above the ground. They cannot be affected by matter or energy and cannot be killed, but are easy to avoid in most circumstances.
Moodlights are mindless collections of emotion, their colour indicating what emotion they contain. They have no will or sentience and are not malicious or intentionally harmful.
However any creature that comes into contact with the sphere is immediately overcome by the emotion that makes up the moodlight, such as overwhelming rage, grief or joy. These emotions are induced to a level not naturally possible for a creature and as such will usually leave lingering brain damage. A creature affected by a dose of unnatural grief might be left with a permanent melancholic outlook, for example.
Multiple doses of unnatural emotion induced within a short time period, especially of multiple different emotions, can cause strokes, heart attacks and death.
While they cannot be destroyed, moodlights can be banished by the use of magic rituals.

Nameless

The Nameless are a type of outsider that is undefined. They are a walking flaw, living change. They constantly shift in shape and power, adapting to their environment by manipulating fundamental forces and aspects of reality, taking advantage of the ruleset of the brass realms and using it to their advantage. As such a nameless can be an indestructable statue one moment, an unstoppable beam of light the next, a force of crushing gravity afterwards, a cloud of lightning and so on. They shift constantly and involuntarily, but their powers are always extreme.
However their undefined nature is both their greatest strength and their biggest weakness; it is possible to strip them of their power simply by giving them a name or calling them something. If a nameless is called something, even unknowingly, it is forced to conform to its new name in both shape and power and loses its ability to change on its own.
It is possible to define it as nearly anthing, including declaring it to be already dead or to not exist at all.
On the other hand, it is also possible that a story spreads from a survivor, and they tell the tale again and again, embellishing each time and unknowingly making the monster stronger with each telling.
However most of the time the nameless are transformed into various horrific monsters as people make up rumours about them. As an example: a nameless appears on a world and wanders across the land causing widespread devastation and leaving no survivors. People, finding the ruined villages it leaves behind, declare the disaster must have been caused by a dragon. The story spreads, and every time it is told the nameless becomes more draconic and loses more of its powers until it becomes a dragon in full.

Silver dancers

Uniquely among outsiders, some Silver Dancers were once mortals.
A silver dancer is a creature seemingly made of metallic scar tissue. Every time one is injured or it finds itself unable to deal with a situation, the creature rapidly regenerates and changes to improve and better suit their current environment and situation. This includes physical mutations such as growing additional limbs or claws or becoming faster, tougher and stronger, but also more abstract things such as becoming better at learning new information or reading others' expressions and body language. Every change is positive and stays with them forever.
They are thus intelligent, supremely confident in their own abilities, speak with hauntingly beautiful voices and move with such an unnatural grace that their constant movement is usually compared to dancing, thus their name. They never sleep, never tire, never stop fighting and they never, never, never stop moving.
If they are ever made to stop struggling, improving, dancing and moving, they cease to be.

Temporal stalkers

Temporal stalkers that do not follow linear time. They are capable of time travel to a limited extent while inside the brass realms, going backwards in time to try to influence the present and future.
Whilst they have no greater ambitions apart of procuring prey and defending their chosen territory and period in time, they are nevertheless anathema to the structure of the realms and highly dangerous.
Temporal stalkers take the shape of lanky, grey-black dog-like creatures without eyes.

Voiceless Dead

Voiceless dead are a paradox, a living void, an absence with sentience and will. They have no physical form, but their presence is discernible by their movements as they freeze their surroundings and their prey solid.
They speak in silence, they erase noise instead of creating it. Some rare mortals that have learned to do the same sometimes use them as assassins.
The voiceless dead wish for the brass realms to become static, unchanging, frozen forever. They forever work towards this end if left to their own devices, but their efforts are never irreversible, and they themselves are banished by sunlight.

Walkers

Perhaps the most dangerous of all outsiders, the walkers are subtle. They can possess people or corpses and slowly worm themselves into positions of importance to then cause havok.

They arrange plots to free chaotic beings, sabotage magical artifacts, incite wars that kill important individuals and generally just make sure that any situation that could spiral out of control, will do so. Walkers are able to coordinate with each-other through unknown means and thus coordinate complex chains of events to cause massive chaos. They were able to cause major events such as the War of Burning Skies in the past.
Walkers can conceal themselves sufficiently to hide their aura of unease, unless they choose to reveal themselves. The only way to reliably identify a Walker or Walker-possessed individual is to examine their very soul in detail, an ability restricted to powerful Spirits or particularly insane mortals.
Lacking this ability, when mortals confront walkers, it is after extensive investigation work, collecting of evide,ce narrowing of suspects and leaps of logic. It requires confronting a person that seems perfectly ordinary, friendly and harmless, because they are none of those things.