Tartarus is not designing to torment its inmates, nor does it strive to rehabilitate them. Containment is its sole purpose. Those within it's grasp are considered too dangerous to be kept in any less secure facility. The inmates are usually capable of immense destruction, show no remorse or empathy with their victims, and are almost exclusively extremely long lived. No one is sentenced to incarceration within this realm lightly. Each cell is custom made to hold its resident for eternity, if necessary. Reform is possible, but unlikely. It is rarely sought, and those who are sincere and honestly strive to earn it are rarer still. Escape is said to be impossible, but given eternity, can that be truly said of anything.
The creature burst from its stupor, suddenly aware of the world around it. Usually decades would pass between awakenings, but the last few years had been bizarrely full of activity. It breathed deeply, tasting both the air and the aether, after all it was a creature of both. It tasted sweeter than normal, filled with fear and desperation. It took all the willpower the creature had not to give in to its hunger and feed. This starvation was self imposed, there was more than enough of its food emitted by the other inmates to satisfy the creatures needs, but weakening itself was all part of its escape plan. It had long ago damaged the magical containment binding it hear. Only enough to make a tiny crack, but it suffice if some outer force also caused the seal to weaken, combined with an Equestria wide surge of despair. Such circumstances were unlikely but the fiend had eternity, and freedom would be worth however many centuries of waiting.
There were several events that had come close, and each carried a different name across the aether, cried into the darkness by ponies filled with woe. Long, long ago, the names Discord, Tirek, Sombra and Nightmare Moon, had coincided with moments of weakness. Each time the shield had flickered and developed a new flaw by the tiny crack. Nightmare Moon had been especially significant for some unknown reason. Strangely these names had started repeating in the last few years, along with the word Changeling and Chrysalis. This disturbance carried the name Tirek. It was particularly promising. One more could be enough, if it happened soon enough. The surge of fear was still rising. The creature focused on directing all the energy it could feel into the imperfection, forcing it with immense patience and unbending will.
It was not long later, almost a blink of an eye compared to the time the creature had spent locked away, hours, possibly even days, that the moment arrived. The misery of the nation reached a peak. The shield fluxed once more. The gap appeared, and the creature forced itself through, before its cell reasserted itself. The despair in the air was gone, now replaced with the sickening taste of joy and relief. The crisis had passed, but the creature cared little. It was free. It fed on the little it could here, but was careful not to grow too strong within this realm, lest the guard dog Cerberus sense its presence. It would need to find easy prey, something not too far, somewhere among the ponies.
The filly swam through a vault of bits. Then she was in the school yard. Her class mates bowed before her. Apple Bloom and her idiot friends prostrated themselves upon the floor and sang her praises. Now she was an alicorn in Canterlot castle garden, having tea with the princesses. She knew it was all a dream. She could always tell, and loved the sense of control it gave her. She delighted in using magic, and flying through the sky, in being adored, and popular. The world blurred as she visited her favourite memories. Those of the few days a year that she truly had her fathers attention, no meetings, no paperwork, and no business.
Something was wrong. She was in her house. She heard the heart breaking voice of a mare long gone. Her pink coat and purple hair achingly familiar. She didn't want to remember this. She didn't want to be here. She was in control. She had to be. Panic was setting in. She shouted for her father, crying for his help. To be away from her, to get anywhere but here.
She felt the world shift, and her wish was granted. She was alone, and in darkness. She wasn't afraid. She would figure it out. It was only a dream after all, and dreams can't hurt anyone.
"I am going to be okay. I know who I am. I am always in control. Dreams aren't real," Diamond whispered shrouded in shadows. "It doesn't hurt. Nothing can hurt me. I don't need anyone. I am Diamond Tiara. I know who I am."
Randolph always awoke before the dawn. There was always much to do in the mornings of the household. Filthy rich would be up in an hour, and his bath would need to be filled and breakfast prepared. Diamond Tiara always asked to be woken, so that she might share their precious little time together, but the master insisted she get a full night of rest. As head butler, Randolph had no choice but to follow his orders. Though he always checked in on the young mistress, in case she happened to have risen with the sun. He was passing by her room when he heard her shout. she rushed to her room. She had not suffered a nightmare in years, but whenever they did happen they were always deeply disturbing for her.
He opened the door slowly, not wanting to scare her further. In the dim light from the hallway he peered around the room, but Diamond was nowhere to be seen. He checked the room again fully, before running back into the hallway. It might be nothing, but he couldn't take the risk.
The sun was rising over Ponyville as Filthy Rich and his staff ran through the streets, looking for their little lost filly. Meetings would be cancelled, money would be lost, but none of that mattered, not with his angel gone. It was outside Sugar Cube Corner that he saw the grey pegasus swooping over the town's buildings. Her eyes were filled with worry, as she frantically searched for something. He recognised her as the mailmare, Miss Hooves.
"Dinky, Muffin, where are you?" she cried. "I'm coming darling. I'll find you!"
He waved to her, trying to get her attention. That was when he noticed the other ponies frantically searching. A moment later he recognised them too. The parents of other foals in his daughter's class.
"Miss Hooves, can you wake Miss Cheerilee and bring her to the castle?" Filthy called to the panicked mailmare. "Diamond has also disappeared, and I don't think our daughters are the only ones. Princess Twilight is our best hope, and I don't know every family with foals in Ponyville but their teacher will. I'll spread the word to the others in the street and I'll meet you there."
Derpy nodded and flew faster than most of the townsfolk would have thought her able. Filthy ran with all his might. Passing the news to the other searching ponies. He did not want to think of what cruel fate his daughter might be suffering, but thoughts of deranged unicorns, Everfree monster or some other evil laid siege to his mind. He pushed them back as best he could, focusing on saving his little girl.
Diamond was in the dark room. It's walls cold, feeling like glass to her hooves, seemed like panels, slightly thinner than most doorways. She lost count of the panels, unsure of when she completed a circuit of the room. The frustration of wandering in the dark made her forget her fear, as her anger asserted itself. She wrestled for control of her dream back, and willed light into the room. She screamed with fury, her head pounded as she forced her will upon the world around her. A dim glow came from nowhere in particular, rewarding her efforts. Her smile of triumph was brief as she took in her surroundings. The cold glass panels were mirrors and in each she saw herself staring back, terror upon their faces. Her reflections mirrored her expressions, but each was subtly wrong, and yet, she knew that the fear was real.
Princess Twilight Sparkle heard knocks and shouts echoing through her home. She rolled in her bed, willing away the start of the day. The din persisted, and she braved one eye open, glancing at her windows. It was barely dawn. There was no reason anyone should be woken at this unwholesome hour after a late night of studying the day previous. She could feel some thought struggling to be heard, some reason she should crawl from her soft warm bed and take action. After mere seconds that felt like hours the idea took form. Perhaps the reason she was being woken was because something was wrong, something so bad that the townsfolk had run to the highest local authority, a princess of Equestria and an Alicorn to boot. There was something terribly wrong. It took less than a second for that thought to silence all others. Her eyes sprung open and she ran as fast as she could towards her front door.
She grabbed her doors in her magic and pulled them open. She was greeted with the distraught faces of a sizable crowd of ponies. They were all speaking at once. She couldn't make out their words. Raising her hoof she called for silence.
Filthy Rich stepped forward and spoke with forced calm, "Princess, someone or something has taken our foals. You have to help us, I beg you."
In Canterlot, Princess Luna had just finished lowering the moon. It had been a busy night. Many ponies were still having nightmares since the return and defeat of Tirek. Being without magic, strength or cutie mark had left its mark on many ponies. They needed her help and counsel in overcoming this trauma. Such nightmares were not uncommon since her return, especially with each new force threatening Equestria had revealed itself. It would take months before the worst psychological scars would truly start to heal, and for the deepest affected it could even be years.
She scanned the dreamscape again, hoping to find those ponies that worked through the night, who might need her help. She would have breakfast with her sister soon, and perform her final duties for the day before she took her rest. She had just soothed a poor crystal filly revisited by memories of Sombra's reign when she felt something terribly wrong, but the sensation only lasted a moment. It came from Ponyville, and had felt oddly familiar. She jumped from her balcony and spread her wings. She hoped she was wrong, that she imagined it, but she had to talk with her sister, and if necessary contact Twilight.