to be placed in a book later

Vampires:
When Eternia was created by Kraus, and the first Humans roamed its fresh landscape, erecting wonderful towns, creating the first civilizations, there was true world peace. But, nothing so beautiful can last so long as Humans hold Greed in their heart. Cain and Able, brothers by blood, lived in a country known as “Aproporyia”, when the first civilization was created there, High Angel Malziel granted Able leadership of it by divine decree. But, Cain was the eldest of the siblings, and was insulted by this. He has been undermined by this decree, for he was the eldest and demanded the spoils for himself. This caused a tremendous shift in the eldest sibling, who sought out the power to usurp his brother Able. Feeling the taint of corruption inside of Cain, Belial cursed him with immense strength, regeneration, insatiable hunger and bloodlust. Along with the ability to spread this gift of Vampirism to a wider population. With these powers, Cain turned all of Able’s Counts against him, and killed his younger brother. This could very likely be the first time Belial played with the hearts and minds of Humans, though it is uncertain if this is fully true.
Some say that Azrael was the first to taint Cain with a precursor of Necromancy, but from what I’ve gathered, that’s far from the truth.
Necromancy was created by Belial, and Azrael simply copied the formula and changed it enough to suit his own needs.
Vampires may not follow the Word of Belial widely, but it has been known that small covens of vampires have set established themselves as Belialites in order to unlock stronger curses from the Sealed Akuma. Somehow, even Vampires gained the ability to cast magic through Belial’s curses.. Should a Cult of Belial consisting of Vampires rise up. It is extremely wise to crush it immediately, otherwise it won’t take long for them to overrun an entire continent.

Mimics:
This is only a theory. But from what I’ve gathered, Mimics are directly linked to Belial in some capacity or another. Maybe not directly through the magic they use or their belief system, but in how they are made. Their creation is formed when a “Plague Meteor” impacts a large deposit of Orchalicum. The Meteors are directly impacted by Beacons that are on the Moon. One of these Beacons I directly came into contact with when I went on an exploration to the Moon, it was a megalithic structure that would rival the most advanced creation that Barsburg could come up with ten-fold. The Beacon will fire a large beam into space, which will draw meteors to it, their direct course is impacted and the meteors will be forced to go through the beam. Once this happens, the Meteor will be corrupted, into a twisted version of its former self. From there, it will fall to Eternia’s surface. The chance of it impacting even the most Minute amount of Orchalicum is low, but possible nonetheless as we’ve seen on a few continents. Thus, this creates Mimics. Which sole purpose seems to be to expand their reach, cause chaos and kill off any and all life on a continent. Seen on Valmasia, they will slowly begin to convert the land into their own mass. Eternally corrupting it.
If you see a Mimic, they are able to be taught, and trained to not be horrible monstrosities, it’s best to examine and learn their behavior. And allow them to do the same to you. They are capable of feeling, learning and growing. They are not inherently evil, unless they are directly linked to a Doppleganger.

Apostles, Wardens of the Nightmare:
The direct link to Belial and his Followers. These beings are wholly manipulative, and will tell mortals exactly what they want to hear in all situations. My guess is they can sense exactly what you want out of life, and form their sentences based on your deepest desires. This is done so the followers continue to give themselves to Belial, and use his corrupting power. So he may have mortals to conduct his rituals and sacrifices Eternia-side.
They only exist for the purpose of corrupting the vulnerable. According to the Holy Book of Belial I obtained on one of my journeys, it is possible for a mortal to become an Apostle by giving themselves fully to Belial, by conducting a highly secretive ritual that may see the death of hundreds, maybe even thousands within a single night. Their of the sacrificed souls will be corrupted to such a degree that they won’t even be able to be shaped by the Angels after death. Instead, they will be gifted to Belial as a *snack*.
And the freshly created Apostle will be granted unimaginable power, at the cost of their old selves and their own soul. Their body will be pealed away, and in its place will be a shadowy shapeless figure, completely void of emotion, or apathy. From this moment on, there is no saving these creatures. Their fates are sealed by ritual, death and destruction are certain wherever they tread.
Known Apostles:

Nantosuelta the Fifteenth “Reaper Apostle” - Status Unknown, Roaming Aegis as of 1835.
Takes the form of a Feminine figure, likely to throw off its victums. This particular Apostle has been known to go to Cults Of Belial that have been swaying from their unholy path, and slaughter them. In the year 1830 it was summoned to Crescent Moon Island, and slaughtered the entire cult there on sight. As, this cult allowed the Death of a Moon Diamon, Vastator, and failed to protect a piece of the Moon that resided on the Island. Thusly, they were punished. In the year 1835, a Summoning Ritual was preformed on Crescent Moon Island, which released it onto Aegis to roam freely.

Marrowit The Twelfth “Midnight Apostle” - KIA, hasn't been seen since the late 900's.
This Apostle didn't always stick to one form. It's noted to always shift into something more desirable depending on the people in its proximity. From what ancient lore states, Marrowit was one of Belial's most trusted Apostles, and was used as a type of envoy. Sent on diplomatic missions to sew fateful deceit in the hearts of mortals. It was not the strongest of the Apostles, but it was likely the smoothest talker. Everything was a lie, and nothing was true. It's also stated that it was unusually easy to achieve symbiosis with. And would taint those who did achieve symbiosis, gifting them some kind of unknown decay that would rot the skin, bone and soul.

Ossein The Seventh “Marrow Apostle”
The majority of the lore on this Apostle is lost to history. Everything but the name and title. Likely has something to do with bones.

Sugriva The Sixth “Scribe Apostle”
Everything about this Apostle is lost to history. Assumed to be a scribe of sorts, according to its title.

Nyxtilria The Daughter “Shadow Apostle” - Status Unknown. Supposedly living on Aegis.
The lore on this particular Apostle is a mystery. They call her The Daughter and Shadow Apostle, so it can be assumed that they are a direct descendant of Belial to some capacity? The truth is unclear as to why this Apostle has this title.
Edit: It is entirely possible that Nyxtilria is actually “Nyx”, of the Cult of Nyx. Though this has yet to be proven.

Prophets of the Nightmare:
Not much is known about the Prophets, as there has only been a single occurrence of mortal men coming into contact with these otherworldly beings. They are said to be the Prophets of Belial’s Word, each of them in life claimed the title of Prophet, fully succumbed to Belial’s Curse, and when they died, their soul was remolded by Belial into something more. Their appearance resembles that of an Apostle, but with two key differences. Rather than the blackened tar form that the majority of Apostles take, Prophets are a bright crimson color, and the form itself is tar-like, just like the normal Apostles. And sport an unholy hat that is said to grant them powers to control Diamon’s and Beasts of the Moon, as a type of rallying device. By the names and titles of these Prophets, it is entirely reasonable to believe that each Prophet is attached in someway to a limb or body part of Belial. Whatever the inclinations of this mean, is unknown.
Known Prophets of the Nightmare:
Yuzilrath The Unending "Prophet of Ears" - Status Unknown.

Hirano The Horned “Prophet of Head” - Status Unknown.

Kreldara The Fingers “Prophet of Hands” - Status Unknown.

Belithar The Heart “Prophet of Body”



Souls of The Forsaken:
Death at the hands of an Apostle is a truly dreadful fate. For when you die at the hands of one of Belial’s most faithful, your soul is forced out of your body, and sent to the Moon for reshaping. From this moment onward, your soul will be unable to move onto the next stage before reincarnation, it will never see the holy glow of the Lifestream.
Instead, what happens is your soul is mashed together with potentially hundreds of other souls, and corrupted from there. Your very soul will take on a physical, twisted shape, akin to your most dreaded nightmares. Pain and suffering will be your only existence from this moment on. And should the physical form “die”, your soul will then be gifted to Belial, eaten and swallowed as a energy source.. As recently as 1835, over three hundred souls were taken by the “Reaper Apostle”, Nantosuelta on Crescent Moon Island, off the East Coast of Esshar. This is potentially enough to create a massive monstrosity, only capable of destruction.
All who undertake the Initiation Ritual, and give themselves to Belial fully, will likely suffer this fate as well, unless they Cleanse themselves of his curse.

Moon Beasts:
Mindless, empty creatures helbent on destruction. They do not have the capacity to think, instead acting entirely on base instinct. Which obviously, is slaughter and consumption. But the weird thing is, they do not require sustenance to exist. They eat simply because they have the ability to do so.
These beings take many shapes and sizes, much like the Demonkind of Eternia. Each one I’ve encountered has had the ability to take on up to five magi at a time and still come out on top. Mindless, but extremely powerful.
Outsmart them, before they outmaneuver you.
Known Beasts by name:
Fred - Soul Trapped.

Moon Diamons:
Guardians of the Seal.
The Moon is a horrific place. Hundreds, potentially thousands of these Diamons roam its surface, searching for intruders, souls to consume in order to gain more powerful. Some are as small as a frog, where others are the size of mountains. Strength varies heavily, depending on how many Souls of The Forsaken have been consumed since their creation. How these beings come to be, is currently unknown. But after finding vats of biological material inside one of the Beacons on the Moon, its entirely possible that these are created by unknown sciences, and twisted arcane magic from Belial's Void Serraphs, from Humans, to Diamons. They're intelligent, but appear to be in constant pain, and are always screaming due to this. So, from first glance it would be hard for anyone to truly understand that it is a sentient creature. During my youth, I actually summoned one of these Diamons with a Belial Ritual, and assisted in slaying it. It was no match for me and my group, but if I were alone, it would have most definitely ate me whole.
Known Diamons by name:
Vastator - KIA, Body Destroyed.
Mezrikdal - KIA, Body Destroyed
Krendril - MIA, Got Away.

Dread Vanguard Golem:
According to the lore I’ve found that relates to the Cult of Belial in Valmasia, when they had their first encounters with Belial, cosmic titans rained from the sky, approximately a dozen of these beings had fallen from the Moon to Valmasia. The exact nature and role of these titans is unclear, as this event happened almost a thousand years ago and the writings have long since burned or lost. My theory is that these beings are the vanguards of Belial’s invasion, but is unclear. Maybe to sow doubt in mortals, and make them seek the truth about what resides in the Moon? Whatever the case, should these Golems fall from the sky, it is clear that Death and Destruction will soon follow.
Approximately one hundred feet tall, and thirty feet wide.

Void Serraphs:
Since Belial has been locked away inside the Moon almost two millennia ago, Angels from Avalon have watched over its Lunar surface. Guarding ever so vigilantly so any who wish to free the Akuma might be stopped. However, what is not known is that Angels are also not safe from the unimaginable corrupting power that is Belial. These beings, once the Guardians of the Moon, have turned and are now it’s most valiant defenders.. Their entire being is twisted, and warped into something that hardly can even be recognized as an Angel. The main body of this once holy arcane being, is now mostly bone, shredded to pieces by unknown past events. Four skeletal blackened wings span almost a hundred feet from beginning to end. Unknown crimson liquid continually gushes from open wounds, with a thickness akin to tar. And, a screeching voice that could shatter bones and sink deep into your soul.
The Void Serraph that my group had encountered also wielded an infected version of arcane magics, like this world has never seen. Where normal arcane seems to be mostly described as pure and white, this was the exact opposite. Black, horribly depraved magics that made one feel like death was right behind them.. Additionally, it had an odd form of Mana Absorption! Who would have thought?

Void Parasites:
Microscopic organisms that feast upon a Magi’s mana, blood, flesh and the marrow in bones. These are likely one of the most destructive parasites found to date. They originated on the Moon, and from there were warped heavily by the Akuma’s divine magic, turning them into an unstoppable hive of destruction. If you so much as get a single parasite inside your body, you may as well just end your life, as they will rapidly multiply at an alarming rate and get into every part of your body, including heart and brain. However, there has been a treatment found that can assist in “freezing” the parasites so they spread slows significantly.

Moonstone Colossus / Frozen Flame / High Angel Marciel
Once more, an Angel that has fallen to Belial’s curse, eternally bound to be one of his most loyal servants. Unlike the Void Serraph, this Angel was of an entirely different breed; for at one point in time it was known as High Angel Marciel, once said to be the most passionate and most Human-like of all Angel-kind. And now this once holy being can’t even be considered anything but pure chaos. Luckily, Marciel has been put out of her mystery once and for all, as it’s body and essence was incinerated by the combined mana of twelve of Moxtil’s strongest Magi; who created a ball of mana so incredibly potent, that it simply erased any trace of the once High Angel from existence.
There was two forms of this being.
First, was the form I consider the Moonstone Colossus. It’s exterior layer was a colossal mass of angelic wings corrupted by Belial’s curse, black as the void, and wrapped loosely around the Angel’s body, which remained encased inside its inner layer. Eyes jutted out in all directions from the mass of feathers, always watching.
Once the outer layer was burned away, it was shed its feathers and fell to the ground.
This was a truly horrible sight. It can only be described as Demonic in nature, it’s only holy form has been warped into looking more akin to that of a Yokai of Mordred’s Brood. Horribly distorted in its appearance from potentially over a millennia of corruption. It’s arcane magic was not the same as the Void Serraph either, it was truly directly linked to the Akuma’s dreaded celestial mana. Unholy and ultimately destructive in all respects. Simply being around it was maddening, and being hit by it was like having your soul directly attacked. Shedding it away slowly.
High Angel Marciel may rest easy now.

The Cardinals:
There is little to no information on these abominations. Only a single passage in the Writ of Belial states “- and they who will lead the holy crusade against the non-believers, shall be righteous and bring ultimate destruction. The Cardinal’s fury knows no end.” It is unknown if there is more than a single Cardinal, but it can be assumed that there is more than one, as they use “Cardinal’s”, plural. These beings very likely Belial’s highest generals, and will lead the charge against Eternia, of Belial is freed from his imprisonment.

Death’s Hand:
The true incarnations of Death personified.

Avatar of Belial:
Likely just Belial's Mana taking a physical form on the mortal realm.

Belial:
According to the Creation Myths, Belial is an Akuma created by the ‘God of Atmos’, with a single purpose in mind. Destruction. Everything that ever was or could be, must be wiped from existence, or else it’s very purpose for existing is null and void. The only thing that Belial wants is for all to be consumed, not even his own followers are safe from his endless hunger. Though this is uncertain, it is theoretically possible that Akuma are far stronger than Angels, possibly even Arch Angels, like Kraus.