It was so long since he'd been able to do more than think, but soon the plan would be set in motion. Deep in the Everfree forest, in the deserted Castle of the Alicorn Sisters, the silence that had fallen over the area was shattered by the grating sound of metal on stone. Scattered off the dais, the midnight armor glowed with ethereal power, the mind within pulling the ambient energy surging through the old castle and using it to animate the vessel of his soul.
The first surge that had passed over him had taken him by surprise, and was over before he could react. He would not let the opportunity pass a second time. Using the mana suffusing the area, he imposed his will upon it, and runes were emblazoned onto the inside of the armor.
Mana Storage, so that he would have something to work with even after the surge.
Ambient Mana Absorption, so that his body would not fail in its task.
Animation, so that he could once again move among the living.
The surge passed quickly just as it had before, but his goals were achieved. He had no way of knowing how much time had passed, nor did he care. The lives of his people, his species, his world, even the Gods demanded the dark one's blood.
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He'd been so close to completing his rite, the ritual hunt that would separate him from the rest of his clutch-brothers. He was wandering the plains when he'd first seen her. Out of a vortex of impossible colors and shapes emerged a broken and torn quadruped, bleeding heavily and missing a few limbs if the stumps were anything to go by. Curiosity won out, and the hatchling had approached the creature, wondering what it was, and if, as honor would demand, assistance could be offered. Even as he spoke up to offer assistance, it's empty eyes had fallen upon him, and it began muttering in a strangely pitched language, before it faded into a mist and rushed at him.
The next thing the hatchling was aware of was excruciating agony, as the dark goddess took hold of his body, and used it to remake her own. The shining scales he was so proud of were burned away, his tail repurposed to repair her terrible wings. What was not used, was left to the soul-fire, a burning power which converted the very mass of his existence into mana. But the hatchling did not die. Death would have been preferable though, to what awaited him.
The very next moment he became aware of the broken chorus, an unholy multitude of voices, some screaming, others weeping, others snarling in a blazing rage. He tried to cry out, to be heard. He demanded she stop, even as she set fire to his village. She did not recognize his people as sapient, they were merely animals to her. He heard them say so, calling his people useful creatures, if only for the energy needed to return home. She did not hear his pleas, lost as they were in the chorus of her broken mind. So she continued, and he watched her burn it all. His people, cities that surpassed anything he had seen before, creatures of myth so terrible even in his agony he felt fear, even the gods themselves burned in her unholy fire. He watched it all, and wept. She had taken it all from him, and not even had the courtesy to realize what she had done. When she opened a portal to her own home, he realized that it was not over. The hatchling was still trapped in the Dark One, like a beetle stuck in the mane of a Sseretson. He watched as she returned to her home, restored to her full strength by the burning of his world, and proceeded to once more wage war against her sister.
He watched as the elder sister wielded strange stones of power. The were not unlike those the heroes of legends of his people used against the great evils. The elder sister sealed them both away for so long. He watched as the Dark One returned only to begin again, attempting to cast the world into the long cold once more, only to be stopped by six young females wielding those same stones of power, finally separating him from the mad goddess. And he watched, with unmatched fury, as the elder sister forgave the dark goddess. No, magic stones didn't cleanse her of the blood she had shed. The elder sister had no right to make such decisions. He attempted to stand up, to voice his grievances, to make the dark one answer for her crimes, but he found movement impossible. He tried again, and again, each effort serving to further fuel his growing rage. Each attempt was as unsuccessful as the last. Only long after they had left, to his eternal ire, did an animal of this world reveal to him why he was unable to move.
A careless paw had struck him in the head, shifting his view so that he was facing the rest of his body, or what was serving as such. The armor of the dark goddess. Even as she was granted freedom from her own crimes, he was left to suffer. But he would not do so quietly. So he studied. He felt the energy flowing through the air, he thought back on the times he'd felt the Dark One use her foul magic, and he studied the memories. Like the great hunters of #S%)XE@~ he would use his preys own strength against her, he would honor the Gods of @#$D$E^%F by bringing Just Wrath upon her.
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Even as the hatchlings memories failed, his resolve only strengthened, and when the day came that he was free, he opened his eyes again to the true world, moving his head of his own accord for the first time in years. His form was altered, as he'd expected upon regaining control. There was nothing left of his old form, as he gazed upon the lithe shadows that inhabited the armor. No, glancing at a broken mirror off to the side, he realized he was left with one thing, the only true reminder of his people.
His teal, reptilian eyes remained the same. The eyes she had stolen from him, using in the place of those she'd lost, and using them to strike fear into her enemies. Now they would do the same to her, they would be the reminder of her sins. They would be the herald of her death. Picking himself up off of the ground, he wasted no time in looking for the library. He knew her words now, being trapped in her mind so long had left him with such knowledge, and he would learn of her world. He would prepare for this hunt like his people had done from the beginning of time. Study your prey, learn the weaknesses, exploit them. Strike when your prey least suspects.
The hatchling realized something as he stalked the halls. He'd...forgotten his name. H-he needed a title. Only those who completed the Rite could grant themselves new names, but with the destruction of so much, perhaps... perhaps the God of Vengeance would allow it. It would be a fitting end to the Dark One, and bring honor one last time to Blood Seeker's name. Yes, Blood Seeker, God of Honorable Vengeance. He would make his people proud, allow them to rest easy. There was one last hunt before his people consigned themselves to the long cold. As the empty armor moved through the slowly brightening abandoned hallways, Luna slept in her resplendent tower, blissfully unaware of the wraith that had been unleashed that night. Her mind was too focused on the previous nights festivities, and the wondrous treats the foals had gifted her with the night before.
Author's Note
Idea while pondering the nightmare once more, this one is actually more in line with my personal idea of Luna's madness. I find it easy to see her mind breaking under the stress of years of solitude, though Blood Seeker is just a little something extra to make it interesting. Also gives the explanation of the eyes, so I like that. 
