Grimm

The slow creep of Death

Introduction

One of the most wide spread species on the planet, this species is known for it's hyper aggression everything not it's self and it's parasitic nature against all life on planet. It is unknown exactly how or when the Grimm came into being only that they've been a consistent and existential threat to all life on the planet. Often killing Animals, Humans and Faunus alike with reckless Abandon.
Seemingly simplistic it is easy to underestimate them due to the low level Grimm that are commonly encountered. Their presence Lessens and increases based on time period and in the Current era, Grimm are growing in density and intensity that threatens the safety of everyone. Yet despite their long list of victories against life and the countless deaths they've caused.
They've become normalized and thus under considered, especially when politics and internal divisions bubble up.

History and Significance

Grimm have been present at almost every major period of history, there is many rumours and Myths that surround them and indeed Scientific study of these monsters is made difficult by the fact that they dissolve after death. Leaving behind Essences that could be used for study or for pay and often the latter. The majority of cultures characterize them as Creatures of Destruction or Darkness.
Interestingly some Grimm appear to reference tales from Ferry Tales and some theorize that someone is making them, this was what Whitecliffe Research Centres say, creating various studies and claim that the Grimm are more clever then believed and have a intelligent and malevolent force guiding them. However Atlas' researchers believe that Grimm can only evolve to be intelligent and have nothing guiding them.
Atlas won out, most liken Grimm to big dumb angry monsters who are easy to kill causing others to no longer see them as the World Ending Threat they absolutely are.

Grimm Biology

Grimm are often animal like and possess a wide array of traits with some Grimm creating 'Grimm Pools' which are pools of reflective blood like substances and sometimes inky black Ink like substance where Higher level and lower Level Grimm can grow out of. Despite some opinions Grimm all have Organs and all have Black Blood.
They're able to grow these and regenerate these in Grimm pools and do not age unlike typical living creatures. Grimm notably have extremely high aggression, through the study of live Grimm, Whitecliffe figured out that Grimm have a negative reaction to Serotonin so even positive emotions amp up their aggression. However there are 'Reject Grimm'.

Reject Grimm

When Grimm Form they often do so in spawning nests where they fight other young Grimm to earn the right to exist. Reject Grimm have rarely been captured but when they are, they do not have the same chemical reaction to Serotonin and thus have lower aggression and can be taught but given the difficulty of finding ones still alive, very few people have ever domesticated a Grimm.

Organs and Black Blood

Grimm Eat, Breathe but don't Breed. That means on top of having a natural inclination to violence, Grimm also get hungry and hunt, causing them to attack animals for food. Interestingly Grimm die when they eat each other too much, this is because Black Blood is a poisonous substances making hunting Grimm for game deadly if not already made difficult by the face they dissolve over time when killed.
Thanks to the existence of organs it's possible to kill a Grimm quickly but Grimm are often covered in thick and tough hide with a inky black appearance and Bone armour that is harder the reinforced steel. As a result it normally requires precision strikes or heavy saturation to kill a Grimm.

Death Cycle

Contrary to popular belief, Dissolving is not the only stage of Grimm Death, Atlas & Whitecliffe Scientists have both examined that 'Alpha Grimm' which is the veterened more powerful versions of certain Grimm types. Have Noticed that Alpha Grimm leave behind small Grimm Pools and if enough die in one spot can make a makeshift spawning pool and prolong infestations.
So Fire and Ice are common Dust types people use to safely eliminate such types of Grimm.

Reproduction

Grimm do not reproduce sexually, they lack any form of gentalia as well as any form of sexual desire. Instead Grimm reproduce asexually through the use of spawning pools. Thanks to detailed Drone Surveys of Grimm behaviour, it's discovered that Grimm as they age collect a blood like substance in their bodies, senior Grimm build up enough that they can puke into some kind of natural bowl or some structure they create which then allows 100's of Grimm to quickly form out of the pool.

It is not known exactly how this substance actually creates Grimm or how Grimm grow from it. The average cycle is that every 10 years a senior Grimm would find a new nest and create a new pool which over the years will have a increasing number of Pools and thus worsening the infection. Recently as of 75 AGW, the Reproduction cycle has been observed as changing steadily.

The increase in Grimm has been attributed by the Grimm now contributing their built up 'Blood' into pools together rather then letting alphas do it alone. What this means is that a single pool in the course of 2 years can turn into 20 where before it took 10 years to reach such heights.

Evolutions

Outside of a faster reproductive cycle other evolutions has occurred, Abeline Bright has led multiple projects from White Cliffe that observes that over the years the dissolving period of Death has slowed, this enables Grimm to collect the 'Blood' of other Grimm to create more spawning pools meaning that Grimm can recuperate from huge losses quickly by recycling material from their own corpses.
Other Evolutions include the spread of Farseers...

Atlas believes the Farseers to be the beginning stages of a simplistic Hivemind that enables greater Grimm Coordination but Dr. Bright hypothesizes that a vast Hive mind existed from the start. The Detailed research through the nearly 80 years of Combat data has seen a intelligence increase of all Grimm outside of Astora through the use of Farseers.
This suggests purposeful evolution, noting that Grimm adapt quicker then their brain should hypothetically be capable of. Grimm also have developed greater bullet resistance which is why thumper Rounds have become so widely used across so many hunters of Grimm. Vision and equilibriums have also seen a steady improvement over the thousands of generations of Grimm.
Now more Grimm are gaining the ability to Corrupt and turn living creatures, both Animal and Human against each other and as well as spread Grimm Plague turning the Grimm from a creepy but killable enemy to an undeniable existential threat to all life on the planet and Bright hypnotizes the rest of the Universe once Grimm are finished with Remnant.
Grimm are weak to Psionic Technologies, causing the creation of Whitecliffe's PRISM which creates insane 'white noise' in Psionic networks reverting Grimm even the smarter ones to a primal dumb blood savagery and makes them incapable of strategy. In the past Atlas has used viruses to kill off thousands of Grimm but Bright's studies find that all Grimm have developed highly sophisticated Immune systems making them near immune to all known disease types except for Prions which infection causes Grimm to self terminate and other Grimm to not due their 'Blood' for blood pools.

New types of Grimm have also developed in isolation, spotted by Whitecliffe special forces and Hunters, these unique creatures possess new abilities such as acid spitting and Psionic amplification of Grimm Hiveminds. The Cenitaur is one such Grimm, rarely seen outside of Astora, it's been observed to be some kind of 'experimental' Grimm, which only lends more legitimacy to the idea that the Grimm are controlled by a dark  force that is trying to destroy the world.

Origin/Ancestry

Darkness

Lifespan

Infinite

Geographic Distribution

• Atlas
• Mistral
• Vacuo
• Vale

Related Organizations

• Schnee Dust Company
• The Crimson Legion
• The Institute of Liberties

Humaniod Grimm are rare and are thought to be more intelligent and use levels of strategy depending on the age of the Grimm or perhaps their experience. They smith weapons and harvest the bone armour of lesser Grimm to smith themselves full sets of armour. It is often rumoured that the Humanoid Grimm are descendants of the lost Astoran Army, from the days before the Great War.
However outside of the Fallen Kingdom of Astora, they were a rare sight, until very Recently. (Post Volume 4 Time Skip)

Grimm are typically Region locked until after the Great War where a spread of Species spread across Continents, for instance the Sabertooth Minor was once only found in Vacuo but has since spread to Vale and Mistral with some scouts reporting their existence in Atlas. The Loss of Region locking makes preparing for Grimm Hunts harder as it is now much harder to figure out what you'll be fighting in any engagement with them.

Some Grimm resemble Lizard like creatures from a Long undiscovered age in Remnant's history that was before the existence of Humanity. They are often some of the more ferocious Animal type Grimm you could encounter. This is possibly because the Lizard Creatures were thought to be some kind of Apex predator before they were wiped out by some asteroid storm that ravaged the world 100's upon 100's of years ago.

Winged Grimm are a common hazard, the challenge they present is that they can damage aircraft and effectively chase Hunters while they're trying to kill other Grimm. They often possess ranged attacks such as the Nevemore who can fire massive feathers with razor sharp bony ends that can penetrate through reinforced vehicles and large buildings.

Nightmare Tales tell stories of Astoran Royal Guard who once served a Noble Queen were corrupted by malice and Darkness and turned into Grimm. While it's not common, some people have had parasitic Grimm infect them with some kind of Plague that turns people into Grimm through the use of Nightmares, aggressive mutations and worse. That said it is rare, Until now (Post Volume 4 Time Skip)
Grimm Plague 

Some Grimm like the Apathy or otherwise known as 'Grimm Boneys' have mastered the ability to nearly mind control Humans and Animals, the Apathy reduces your positive traits and exaggerates your negative ones. Long term exposure to the Apathy can render permanent changes to people meaning victims if they survive could go on to sow discord in society and weaken society and make them easier prey for other Grimm.
If you cannot escape, the Apathy will reduce you to a apathetic close to comatose state where they'll take you and eat you.