There is a rather graphic description later on in the chapter to forewarn you.
Chapter Two: A Drop of Magic
Clouds whizzed by at dizzying speeds. Wind blustered against the mare's face, warping around her sleek black fur. Her many colored mane wiped around, tangling in her tail. Chaos Strider had hated her father deeply when he told her of her marriage arrangements. She didn't even know the stallion he sold her to. She hated him even more when he told her she couldn't retain her draconequus form. The twisted brand that many mistook for a cutie mark solidified her in alicorn form. The transformation was painful like colt birth. She was shattered and reformed. Despite this however, she never despaired. Chaos refused to be broken. The open sky was freedom. This much at least she could be thankful for.
The tangle of Etena stretched impossibly long beneath her. Dark trees reaching for the sunlight with desperation. A world not made for pony kind. Animals hunted and foraged. Took care of themselves, deformed by wild magic into monsters. Timber wolves, stone crocodiles, manticores, and other such creatures, just to name a few. She savoured the chaos rising from the forest's collective breath. Nature was warped by chaos but there was order in it still, the strong fed on the week, the stronger fed on the strong. The savage civilization of the woods. Strider breathed deep, slowing just a bit, enjoying the pleasant burn of the sun on her skin. With a flip of finality she turned sharply North and sped off, a burst of sound in her wake.
*pov
Twilight sat bolt upright. She had fallen asleep in her library; that hadn't happened for quite some time. "What a strange dream…" However she could no longer recall it. The vague feeling of flying was all that remained. Groggily, she stood, a tome sliding off her back giving a thunderous thump upon landing. She telekinetically grabbed it. The withered leather binding bespoke of lost wisdom. Twilight didn't recognize the book. She had read every one in her collection. Gingerly placing it on her stand the young alicorn began to flip through the inked history. Immediately she noticed that the tome had some sort of encryption or was written in some other language.
The book spited her every attempt to read it with no method or spell giving the slightest hint to be working. Twilight hopped down and paced. The archaic nature of the pages, the clearly handwritten text, this whole scenario stank like one of her teacher's tests. She was far too eager to solve the puzzle. A million spells raced through her mind at once and a she was hit by a sudden spark of inspiration. "I think I have a spell for this."
She leapt back onto the stand's platform and formulated a spell to cast, more aptly a combination of spells that should have the desired effect. Twilight cast the spell with a flourish of her horn. A purple light flashed intensely for a moment before fading away. The princess of friendship gave an exasperated growl when it did not work. The book should be speaking its written word in the voice of its author. The spell had to have done something! Shaking her head slowly twilight took a step back. She had learned her lesson from the last catastrophe caused by her obsessing over something like this. As an alicorn she had even more power and even more responsibility. It was clear that she needed to walk away for a while, maybe she could think of something when she came back.
*pov
Luna and Celestia were meeting with a meeting with a dignitary from the griffon kingdom. On the whole the negotiations were going well. The impressively large griffon bobbed his head with every step. If Luna were a lesser pony, she would not have been able to contain her laughter. The more she listened to his squawking the less she liked him. Celestia show impossible patients with him and Luna found herself marveling at her sister's ability to lead. It was while on a tour of the palace gardens that a sickening feeling sunk in to her mind. The world blurred and tipped dangerously. Panic stabbed at her heart. Her hooves would not respond to her mind's orders. The earth under her burned and cracked, snow flitting down around her, clumping in her fur. "Oh… Oh no." The whisper barely escaping before her throat clenched up.
"Luna!" Celestia was by her side again, momentarily giving her comfort.
"I-it's h-h-happening a-a-a-aga-" forming intelligible words became impossible. Her legs gave out from under her. Celestia taking her weight on her shoulder and guiding Luna gently to the ground. Her older sister's face was nearly invisible in the storms increasing intensity. "N-night-...mare," Luna choked out before Celestia had faded away completely.
She was in the wasteland again, lifting a wing to shield herself from the driving snow. It was impossible to see. The ground crackled and sizzled under hoof steam rising from every inch, yet the cold air bit with all the ferocity of the Crystal kingdoms deep winter. Celestia's voice was very distance and growing fainter, calling her name. Soon her sister's presence had evaporated entirely. Luna was alone, again, in a place where her sister's love could not reach her. "What do you want?" she shouted at the storm. "Why have you taken me?"
As if in response, the torch bearer from before trotted up next to her. He sung his head, silently indicating his wish for her to follow. She did. For the first time in this dream some of her powers worked. The shadow pony would just walk through objects, over open air of a ravine, or on rare occasion cross a bridge that wasn't very stable. She kept pace with him regardless. Long after, or was it soon, they arrived at a large fortress. The six other shadows Luna was familiar with melted out of the darkness and stood in a semicircle around her. Each in turn spoke one word of their tongue and bowed to her. For the first time she understood, they were speaking their names to her. The dragon walked forward and lifted a claw to the fortress vanished. The torch clattered against the packed earth, they were all gone.
Luna lifted the flaming rod with her magic and turned her focus to the building behind her. Large, smooth, stones fitted together perfectly to form the walls. A massive wooden door blocked the portal in. She kicked with all her might. It wouldn't budge. Just as she spread her wings to fly an unseen force pushed her down. For a moment Luna stood unable to discern what her next action should be. She gazed at the flame in her grip. She didn't know what compelled her to snuff the light out but it seemed sensible to her. These were beings of shadow after all, the light was probably unwelcome in their domain.
The little flame sputtered out when she cut off the air. The door swung inward, a gust of foul smelling, dry air rushed out, flooding her nostrils with the scent of decay. Luna swallowed the bile rising in her throat, strongly wishing to gag. Once she had stepped into the tomb like structure the door slammed shut behind her. She jumped despite herself. "Keep it calm Luna," she murmured to herself. Her own hoof steps, clacking off stone was the only response. The inside was made of the same stone, well worn carpets lined halls, and beautifully tapestry hung from ceiling to floor depicting scenes of various alicorns and ponies interacting. Some exclusively featured alicorns embroidered with such detail that they almost seemed to be alive.
It was the tapestry at the end of the hall that caught her attention. It was ripped and sindged in innumerable locations. Luna however recognized what remained of the depicted stallions features. It was the same as she had seen in the memory. The weave was ripped cleanly down the middle, separating the damaged white stallion from a faded black mare. While the white alicorn had been deliberately defaced, his female counterpart seemed to have been neglected entirely. There was a runed plaque just beneath the art. Luna gasped as she found herself able to read it. "Prince Frostfire and Lady Chaos Strider," she sounded out what it said.
"That's right," a raspy voice grated out behind her. The stench of rot permeated the room even more. Luna swallowed carefully before turning to see who had spoken. Had she been a lesser pony she would have shrieked. There before her was the twisted, bloated corpse of a unicorn, his long beard, mane, and tail matted and falling out; lips pulled back, showing horribly rotted teeth; his ash grey coat peeling away from his emaciated, skeletal muscles; part of his eye socket was showing as well as his shoulder blades. His cloudy lifeless eyes stared at her. He spoke the same language as the shadow ponies only this time Luna was able to understand. The princess of the night had many things to ask him.