Awnshegh
The awnshegh, plural awnsheghlien, which literally means "Blood of Darkness" in elfish, are an extremely broad category of monster in Cerilia, the Birthright campaign setting.
Within the setting, a being can be a "blooded" or "blood scion," possessed of supernatural power from fragments of the old gods. The oldest of these old gods was Azrai, the god of lies and darkness whom all the others sacrificed themselves to destroy permanently, and those blooded by Azrai's power often find themselves warped in body, mind, and soul, which is only fitting for a wicked god obsessed with "improving" on the natural order and the progenitor of all beastmen.
An "awnshegh" is a being who was once a scion of Azrai that was twisted out of humanity by their dark power, committed bloodtheft (stealing the power of a blood scion with a deathblow to the heart) on a scion of Azrai, or simply had a particularly strong awnshegh parent. They take a variety of forms, some humanoid, some not. Some were once ordinary people, some were once animals, and some are just fucking weird.
Now, having the blood of Azrai doesn't necessarily make you a villain in and of itself. Indeed, some awnsheghlien aren't even necessarily bad people in their own right. But, the dark power of the Lord of Chaos resists being used responsibly, and while not all of them are evil, most of them are, and none are truly good. (Well, okay, the Banshegh sort of is, but Justina Heughlou is barely an awnshegh.) At the same time, though, many of them are tragic figures: while not all of them struggle with and fight their dark urges, a lot of them are what they are as a result of hard luck rather than bad choices and never asked to be twisted into inhuman monstrosities, and some fight to retain what shreds of their humanity are left.
Awnsheghlien take the place of most "common" monsters in a normal D&D setting. Rather than entire races of monstrous foes for parties to slay for loots, a given awnshegh is a unique, powerful creature, much like the monsters of mythology. Some awnsheghlien produce lesser "spawn" races, either by sexual or asexual reproduction, creating henchmen for parties to fight. And, of course, just like any other scion, awnsheghlien can take up Holdings, bonding to the land and twisting it with their dark power, gaining strength and potency from expanding or cultivating their territory.
Awnsheghlien, being unique and powerful antagonists, have access to powerful blood abilities, including their signature, Azrai-exclusive "bloodform" power, which physically twists the user in accordance with their inner nature as they use their blood powers or gain new ones in a manner beyond the user's control. Azrai's bloodline also has access to lots of good offensive and defensive swag, such as Regeneration and the Invulnerability power, which literally makes it impossible for the user to die unless killed in a specific and unique fashion... and some mysterious awnsheghlien don't have listed means of putting them down for the count.
They were detailed in the Blood Enemies: Abominations of Cerilia sourcebook, which was presented at least partly as an in-universe text reported to the reader by a sage, one who actually compiled lists of research, and even interviews with some of the more-sapient and negotiable ones. As a result, some of its information is fairly incomplete.
There's also a benevolent counterpart to the awnsheghlien called the ehrshegh (ehrsheghlien for the plural), which means "blood of light," though they are generally less common and prominent. The "bloodtrait" power non-Azrai bloodlines possess is something voluntary and controllable, so there's no such thing as an ehrshegh being irreversibly and unwillingly transformed into a hideous monster. Just as an awnshegh isn't necessarily evil, so too is an ehrshegh not necessarily good, though, again, there's a bit of a correlation there.
The Apocalypse
A mysterious, evil cloud, which drifts over the land, in which a hungry bearded face with pointed teeth sometimes appears, sucking the blood and life out of settlements it falls over. It may have been created when a town suffering from a mysterious plague was torched, and thus caused what was once a magical disease to become an atmospheric vampire, or it may, according to an unreliable corpse interrogated under the effects of speak with dead, be the literal breath of Azrai searching for his body. Either way, it's almost impossible to harm by any means (it's not technically immune to magic weapons, but it doesn't even have a listed AC or HP total), and those it comes into contact with it have their blood and life essence sucked out and begin rotting alive over the course of days unless they're given simultaneous remove curse and dispel magic spells. A pretty creepy monster, but not super usable except as an obstacle for a lord to have to try to deal with.
The Banshegh
No, I didn't misspell it. The Banshegh is the first of the more interesting and complex of the awnshegh on this list. By day, Justina Heulough is a just, fair, wise elven noble ruler over her largely human domain in the Mountains of the Silent Watch, and not to put too fine a point on it, an absolutely gorgeous, fuckable woman with a lovely personality, who's done a great job of running the place since her human husband died thirty years ago. By night, the Banshegh rises from her sleeping body and terrorizes her domain and her neighbors, looking like a spectral, translucent blue version of her and appearing in the dreams of her prey, terrifying to death or aging rapidly those it hunts. Unfortunately, while outside her domain the fact that the two are somehow bound together or even the same being is well-documented through the use of spells like locate person that return two simultaneous results, Justine is in denial about the link, putting bounties on the Banshegh and having herself locked into her bedroom from the outside as publicity stunts. And even her own people are torn: Justine would just about be an ideal ruler, if not for the fact that she's got some kind of undead spirit problem she doesn't want to admit even to herself.
How this happened is a subject of much debate. Some scholars theorize that Justina simply has a really off-kilter bloodform manifestation (the Banshegh started showing up shortly after her husband died, suggesting an awakening of sorts), others that the Banshegh is a kind of spiritual parasite, a divine fragment that somehow survived 1,500 years before latching onto a hostess it leaves at night to feed. One source, twenty years old, states that she was cursed by a priest of the dead god Azrai and had her essence bound up with a being from the Shadow World. This is important because the one sure-fire way of getting rid of the Banshegh is killing Justina, which no one really wants to do, and no one's certain what destroying the Banshegh separately would do to her, or even whether it might just destroy their connection and unleash a deadly awnshegh from the one thing restraining it from being even worse.
It's a bit academic, though, as both have the Invulnerability power with no listed method of destruction (though it's also clarified that they do not have the same blood powers, so presumably these methods aren't even necessarily the same as one another). Justina has some powers related to being good at ruling (mostly mind-reading immunity and persuasion), while the Banshegh not only has its dream-entering-age-to-death-through-fear attack, but a standard wail, a withering touch, and a bunch of defensive powers. Definitely a creative monster with an inherent mystery and moral dilemma.
The Basilisk
Once the embittered son of a Khinasi nobleman, or possibly a creation of the same that contained his resentful and poisonous spirit, the Basilisk's mind has degraded into primitive drives over the centuries. He no longer gives interviews, speaks, or has the capacity to cast spells. All it does is hunt, patrol territory, and take sadistic pleasure in torturing prey, for while its intelligence is fully degraded it retains animal cunning. Its once-human form is now a many-armed serpent or lizard, with deadly poison dripping from its claws and fangs and a long tail it can grab enemies with. The toxic slime that coats its body gives it an overpowering B.O., which can be smelt for weeks and carries upwind, crippling and nauseating those who get too close, impairing even those who save and crippling those who don't. Plus, it can turn any water it looks at, up to and including heavy fog, into a nasty poison that drains Strength and Constitution and can even kill outright if not treated. Oh, and it not only has Regeneration, but Invulnerability with no listed method of destruction. Bleh.
While under his father it was a green and pleasant land, as you can easily imagine, given both the psychic influence and literal toxic sabotage of a ruler like this, its domain is a bit of a shithole wasteland. Even while he had a working human mind, he greedily hoarded magic to himself and maintained relentless force over the bandits and giants who lived there. Now that it can no longer control power and rampages about killing and poisoning everything, the only major inhabitants are the Darkblades, a band of political revolutionaries led by a woman claiming to be the rightful sultana of Aftane who may be able to charm the Basilisk with sorcery, since it ignores them, and a hill giant tribe that has given up on trying to kill the creature and just try to keep their livestock out of its rapacious reach.
The Binman
A product of the Chimera's experiments into live and death via alchemy, the Binman was originally an inert mish-mash of parts from various humanoids stitched together. As Danita slew the Iron Troll, however, some of that creature's divine energy soaked into the Binman as well as her, giving it life and animation. In the confusion of its bizarre birth, the creature tore free of its restraints, starting the wizardess down the path to becoming the Chimera, and after attempting to kill her in a brief struggle broke free and now wanders the wider world.
The Binman has no Holding of its own, and wanders the world seeking purpose and true power. It has killed those who challenge it, but has also made friends of both honest men and crooks. Sometimes it works as a mercenary. It is mute, preventing an interview, but some theorize that the creature's slapped-together body has resulted in a jumbled personality, meaning its erratic behavior is the result of different parts and pieces of its mind coming to the fore at different times. It's probably going to end up fighting the Sphinx sooner or later, since it has often fought that creature's armies.
The Boar
Within living memory, a cruel and rapacious nobleman picked a fight with a bunch of druid-priests while despoiling a forest on a hunting expedition and lost. He abandoned his party and fled into the woods, and, like all those who split the party, was struck down by the DM shortly thereafter, as he disturbed a mother boar who gored him to death. Unfortunately for everyone involved, one of her tusks pierced his heart, and the boar in question promptly turned albino and doubled in size, becoming the fearsome awnshegh now known as the Boar of Thuringode. In the years since, many have tried, and failed, to slay the Boar, and every time it successfully kills a would-be hero and feasts on its flesh, it grows in size. It's currently bigger than a house, and strong enough to plow huge sections of woodlands like a clear-cutting logging company in an episode of Captain Planet when it makes a charge and gore attack. It's not truly evil (it's still pretty much just an animal, after all, if a bad-tempered one), but it's a problem for the local druids and a deadly danger to many of the forest's inhabitants.
It doesn't have any real powers beyond monstrous size and strength, Regeneration, and Invulnerability, and, Erik be praised, it does have a suggested method of potential permanent destruction listed. The sage compiling this information theorizes that cutting off its head and removing its tusks might finish it off for good. It doesn't completely control its forest as a Holding, which is still just considered a province of Massenmarch, though its influence has turned it into a spooky and ominous place. The forest is a bit of a haven for bandits, goblins, and gnolls, at least in part because it is one of the few such forests free of human logging and exploitation. Notably, the local druids and dryads are in conflict with the technical owners of the place, who want to get at the choice timber there, and the latter often accuse the former of trying to find a mate for the Boar. This means that while all parties involved want to be rid of the awnshegh, they are still very much in conflict with one another.
The Chimaera
Danita Kusor was once a half-elf wizardess, one who tried to become immortal and eternally young via alchemy and necromancy without using divine power. Perhaps addled by self-experimentation with her elixirs, she theorized that, while no one species could regenerate fully, a blend of various humanoid and non-humanoid factors might let her create a potion that could restore life to a corpse. In the process, she committed several murders, went into exile, and created the a husk of stitched-together parts that she tried to animate with magic and alchemy. After fighting with and killing an awnshegh known as the Iron Troll, both she and her creation absorbed some of its power, causing the latter to animate as the minor awnshegh called the Binman, shattering its restraints and drenching her in mutagenic alchemical sludge. The two struggled before she drove the creature off, but her little dip had already altered her body and mind. Believing that the Iron Troll's death-energy had suffused not only her but every potion in her labrotory, she had the bright idea to make a huge bathtub full of all her mixed together potions, dragon's blood, and the blood of a displacer beast before diving in. What came out was a hideous mismash of half-elf, dragon, and displacer beast, the awnshegh known as the Chimera.
The Chimera is physically and mentally unstable, her beast form shifting over time, a process seemingly exacerbated by killing and absorbing the powers of various heroes who show up trying to get rid of her. Both her forms are capable of speech, though her beast form is considerably more feral and less intelligent, and both are quite mad. She isn't Invulnerable, for a nice change, but she does have Regeneration, enhanced senses, a variety of spells in human form, and a variety of monster powers in beast form, including flight, claws, and fangs. Two of her many limbs always remain as human arms even in beast form, with which she wields daggers and wands. Her transformations are somehow tied to the phases of the moons; her wild mood swings stabilize as the full moon approaches.
Her Holding, the Chimaeron, is mostly governed by a Council of Leaders, town mayors and officials who are largely escaped criminals from other nations and do what she commands when she bothers to involve herself in politics. She controls all Sources within, though, only playing cat and mouse with some wizard brothers for fun. It is a haven for criminals from other nations, including bandits, smugglers, and pirates. Ironically, original incarnation of the Council formed when the locals tried to unite to rid themselves of the Chimera, only for her to co-opt the process to seize control. A nascent ehrshegh (basically an awnshegh of one of the other bloodlines) may be forming in one of the caves, a huge bear-man called the Bruin, who will one day kill the Chimera and drive out the evil that infests the Chimaeron.
The Elf
Despite his title, Rhuobhe is not the progenitor of the elf race in the Birthright setting. He's not even the only elf awnsheghlien - there's at least two others - the Green Man and Rhuovar the Red Bull, and they both work (or worked) for him. He is, however, the very first elfin awnshegh.
Back in the ancient days before the gods battled Azrai, Rhuobhe was one the first elves to welcome humanity to Cerilia in exchange for their aid against the goblins. In fact, Rhuobhe was actually very fond of humanity, at first... which meant he felt all the more betrayed when, after the war was won and elfkind permitted humanity to settle on Cerilia, humanity began ravaging the forests for agriculture and industry. He responded by founding the gheallie Sidhe (literally Hunt of the Elves, more commonly known as the Wild Hunt), an elfin terrorist hate-group that has been trying to drive humanity off of Cerilia with murder, sabotage and catastrophes. He gained his common title of "Manslayer" after his 100th personal kill. But it wasn't enough for Rhuobhe, who subsequently led those elves who thought like him to embrace the dark god Azrai as an ally when Azrai promised to exterminate humanity. Although most of his followers abandoned him when they realized the true extent of Azrai's plans, Rhuobhe remained loyal to the dark god until the bitter end, and subsequently was inundated with his power, becoming the first elfin awnshegh.
Thanks to his blooded powers, Rhuobhe appears as a tall, regal elf whose skin is a shadowy gray color reminiscent of marble and whose eyes have become orbs of solid white. He cannot be harmed by any weapon that isn't at least a +3 enchanted weapon, is immune to "launched missiles" (that is, any projectile weapon that wasn't thrown by hand), and has the Regeneration (minor) and Fear (major) traits. He's a powerful gish with 7th level and Realm spells, who wields a +4 Bastard Sword of Life Stealing and "Winged Death", a +3 longbow that can create its own arrows of radiant blue light that hit as +5 weapons and do +1d6 damage if the target fails a save vs. spell. His blooded powers have increased his senses, allowing him to penetrate subterfuges and illusions, but also means he is near-blinded and disorientated by sunlight - ironically, he's basically become the Cerilia equivalent of a drow!
He rules over a stretch of untamed wilderness known as, simple, Rhuobhe, which lies north of Avanil and south of Boeruine, which he stalks endlessly with his bloodthirsty bands of anti-human followers - such is their zeal that they will even kill other elves for being insufficiently anti-human! Other elven nations don't officially dismiss him, but they don't officially embrace him, either. In fact, they actually look down upon him somewhat, as he is believed to have strayed too far from the elfin devotion to Chaos and become Neutral-aligned, which some amongst the gheallie Sidhe argue makes him no longer fit to be part of their ranks. Of course, few elves are stupid enough to voice such thoughts where Rhuobhe Manslayer can hear them...
Oh, and he still hates goblins. He plans on genociding them next once humanity's out of the way.
The Gorgon
The BBEG of the Birthright setting. Before the war of the gods, Raesene was the eldest son of the First House of Andu, and the elder brother of Haelyn and Roele. However, due to his bastard birth, he was not in line to the throne, something that embittered him despite his family, contrary to what certain politically-tinged fantasy settings might have you expect, embracing him as one of their own. He earned the title "the Black Prince," his armor having turned black and sooty after leaving the court to go have adventures, and became famous as one of the greatest armsmasters of the world, training both his brothers. However, after his father's death, Azrai began to appear to him in dreams and visions, tempting him into damnation by feeding his feelings of thwarted ambition and envy. As the secret champion of the Doom Bringer, Raesene began secretly amassing a private core of loyal supporters and subverting them to the worship of Azrai, before betraying his family and his people in the war against the dark god. After the death of the gods at Mount Deismaar, Raesene was, allegedly, the most powerful inheritor of a fragment of divine energy who did not himself become a god afterwards.
In the years since, he ultimately killed his brother Roele in a final battle, though Roele might've had the last laugh. Raesene underestimated Roele's determination to save his people, and destroying his brother cost him the last dregs of his humanity. Though the creature still believes himself to be Raesene, all that's left is the Gorgon. Also, some folklore suggests that Roele somehow warded or ground out his own power as the dark creature committed bloodtheft on him, forcing the Gorgon to remain confined to his castle and seat of his power for long periods. Either way, no one could ever mistake the stony monster the Gorgon is now for the handsome man he used to be. With a huge, many-horned head filled with ape-like fangs, stony skin bristling with spiky growths, digitigrade legs ending in diamond-hard hooves, and an enormous overall stature, the Gorgon is every inch the monster-king. Additionally, the Gorgon regularly kills and "harvests" bloodlines within the Gorgon's Crown, his huge and ominous Holding, to gain more power for himself.
The Gorgon actually doesn't have Invulnerability, but, well, he was one of the greatest swordsmen in the world before he had a millenium and a half of practice. He also has Regeneration, his stony skin gives him hefty magic resistance and immunity to all but +3 or better magic weapons, and he can kill or turn people to stone by looking at them. The Gorgon is also terribly, terribly patient: after all, he's immortal, as near as anyone can tell, so he's got all the time in the world to plot the downfall and conquest of all other nations. He seeks to become the emperor and absolute master of the entire continent of Cerilia, then of the entire world; his burning ambition is a hot and insatiable thing.
The Gorgon's Crown, his personal Holding, is a huge expanse of volcanic wasteland, riven with seismic activity befitting a ruler with such burning rage and ambition within him. It has a huge mixed military force, with access to gnolls, goblins, and human dregs who flee to the Crown with nowhere else to go, though its military captains struggle to prevent racial hatreds from boiling over. The Gorgon is also in an informal alliance with the Magian and the Raven, with all three planning to overwhelm and destroy all opposition, including all other awnshegh nations, before battling it out among themselves, and has some ties to the Elf. He also has many capable and somewhat-loyal lieutenants working for him, including the wicked dwarf and lesser awnshegh Kiras Earthcore, "the Hand of the Gorgon," Courrak Lone Hunter, an old but wily gnoll chieftain, the Goblin King Charqek Talnos, and a mysterous priestess known only as "the Hand of Azrai," who is not blooded but still a high-level cleric of many dark gods.