My own fantasy, pagan setting happening around 400-300 BC, “Europe”. The times of Iron Age, continental Celtic history, but with mythical beasts and gods actually existing at the fringes of civilization.

Magic also plays a much more real role in the world. Although it is extremely hard to master by mortal beings like regular humans, people have learned to employ some of its essence into everyday life. For instance, “magic” is used during rituals, while praying and interacting with the gods, and as very minor protective spells. An essence can be embedded into a bronze torc in order to protect its wearer by granting them safer (but not entirely safe) passage through the wilderness or greater resilience in battle. Magic is very closely connected with the surrounding nature and people’s bonds with the land and its other beings.

An undead hybrid created magically by a powerful, experienced druid. The function of this creature was solely to protect the tribe’s village and its people. It could not eat, it could not breed, nor have a mind of its own. It could only be commanded by its creator, or by a person the druid has chosen. The hybrid’s life was supported only by necromantic magic, an anti-energy existing alongside the natural magic essense of living beings.

Due to an unforeseen incident, at one point the creature was bonded with a human soul and achieved consciousness, developing a distinct personality.
After the bonding, although his body could now regenerate better, he also became mortal (with a long lifespan, but still, very much mortal). He far outlived his people and was later left to roam the land, becoming a reason for many local legends. He was feared by some, and worshipped by others. Previously reffered to as “the guardian”, or simply “the monster”, he was eventually granted with a new name by other tribes – Arcusios.

Arcusios has features of a few creatures: the height and general posture of a horse, strong hind legs that let him stand upright, long-fingered front paws almost able to grab, and a mostly bare, white skull of a horse with long canines. His body can be covered in scars where previous animals had them (or where the sections were connected), but it’s not entirely necessary. There are three feathers attached to his mane – originally given by his tribe, later replaced with new, painted ones by the people who worship him. He could have more of them, as well as other decorations and paintings on his body applied during festivals.

The creation of Arcucios was preceded by a number of failed experiments. The village folk never admitted to having done these, because necromantic magic was feared and condemned among other tribes. These failed creations died either instantly, or only after a short period of time. Arcusios became the first and only (as it is commonly believed) “working” hybrid that served its purpose. When not in battle with other tribes, it was put to sleep in order to await the next calling.

During one of the attacks, the village could not hold its position. Even with the help of a necromantic beast, the enemy peoples wiped out the village. Arcusios tried to save his creator, but in the moment of the druid’s death, the essence of his life and his magic seeped into the creature as the last resort to save himself. He didn’t know what he wished for, however. The price of toying with necromancy was to have his soul become undead as well, whether he truly wanted it or not.

Their consciousness and personalities melded into one. For a long time after that, Arcusios kept wandering the wilds, feeling lost and broken, trapped in the body of a terrifying creature, having lost everything they had. What was left of their humanity was limited to a scrambled mind, with the animalistic side of them constantly trying to have the upper hand. Still, their pride in creating something so powerful and close to their heart stopped them from cutting that lifeforce short. Instead, they chose to keep fulfilling their purpose of a guardian and a figure of power, protecting the local wilds. Arcusios became more connected to the spiritual dimension of the world around them. Magic became more apparent, more accessible, and way more obviously dangerous.

Throughout his remaining life he met with a number of smaller communities, at first trying to communicate his story and achieve some peace. Most chased him away, others saw the power of gods within him and provided closure. He settled in the wilds close to one of the tribes where magic was the most potent, and made it his lair. Arcusios once again became the protector, the reverent being. He lived through multiple wars and saw many generations rise and fall, feeding off of that energy.

During times of peace, he was dormant in his lair, visited by and cared for by his people until his power was needed again. However, the magic within those wilds changed him year by year, slowly turning him into an immortal, lich-like creature, that would forever sleep and become the new source of energy for others to thrive off of. The tribe has finally fallen at some point Arcusios did not register, others have come and gone, until someone sealed them away, deeming their essence too powerful and dangerous for the outside world. The knowledge of his lair became lost to time, and only the legends remained in local folk tales and songs of a terrifying creature dressed in gold and bronze and coral, ready to wake up when the world needed them most.