The door to Sombra's home magically swung open. The walk to the ambassadors quarters had been a quiet one– not that was unusual of Treeling but Sombra didn't know what to say. He couldn't conceive how the filly had earned him a total reversal of the Queen's decision, but didn't want to question it in front of her. She clearly was not going to side with him on this issue before they disappeared, but after they returned she granted unparalleled latitude.
He looked down to the filly who had followed him the entire way without any prompting. "What exactly happened between you two?" he asked. The filly looked up at him before jabbing her jagged horn into the soft flesh of his flank. "Ouch!" he exclaimed, scowling at the filly whose toothy grin could be seen. "Oh. I see. I'm guessing that trip only had one possible destination then." The rest naturally followed of course, if Treeling could yank the Queen's chain as hard as she yanked his own, then there would have been no other possible outcome of the teleport.
A gilt trip that ended with a guilt trip.
He was genuinely impressed: that type of predator instinct was only born once every few generations. If he could hone it then she could prove a great weapon indeed. "Treeling..." Sombra slowly said, "Your mother taught you a very special skill, and I want to try to teach you another way to use it." Sombra sat her down, and disappeared into his room, before returning with a black cloth. He tied the cloth around her eyes before explaining.
"You can feel magic with all of your senses. Close your eyes and reach out with your other senses to find my magical signature." Sombra took a moment to close the room off to light sources before creating a series of crystals.
One... Two... Three... Nothing, the filly couldn't feel them. "Let’s try something else," he magically whispered into her mind and she turned to face him. Sombra noted that the direct connection could be easily traced while the indirect must be more difficult. They repeated the exercise for an hour and her sensing showed signs of improvement. That was before the house became so saturated with ambient magic that Treeling was blinded to the individual shifts therein.
Sombra was sure that they both knew what she could do with a buildup like that but he was wrong. He had not accounted for the quantities of magic that she was used to working with. Five year old stains created by a singular uses of spells cast by Discord, and the progressive buildup of tiny fragments of wasted energy by Nurse Clarity; they both paled in comparison to what he had given her.
***
The sky flickered above Sombra as he came to. He had been encased in crystal at the epicenter of a devastating explosion where a filly had been fully crystallized on a cellular level. He started to panic and as his lungs burned a faint glow came to his horn. Slowly, he cracked the crystal blocking his face which let in the air he desperately needed. It took several minutes of channeling magic into the crystals that bound him to break them down enough to free himself entirely. They had a fantastically higher density than he had ever created before. They had become so dense that light refracted in them so many times that they glowed black. Another minute passed as Sombra surveyed the scene: one worse than he could have even imagine the filly to be capable of. The blast had extended so far as to resonate off the crystal network he spent five years building.
The sky flickered again. His eyes raised with concern to see the barrier failing. The only way that the barrier could fail would be if the unicorns maintaining it were all killed simultaneously. In five years nopony had known where all of them were, which protected the city, so the only way to get at them would have been exactly this: kill everything. Though it wasn't his intent when he built them, the amplification towers had caused a cascade reaction in the crystallization spell, which in turn extended the magical burst to every corner of the capital. Moments of increased flickering later the shield dropped to reveal that the explosion wasn't contained by it. Rather it shaped a dome around the city that crystals grew out of both on the inside and on the outside.
Sombra took to the streets searching for survivors. The longer he looked the more disheartening the situation became. The first few ponies he came across had their faces locked in contorted terror, which were broken into several shards on the ground, among a pile of their shattered remains. A grimace proceeded the diligent Sombra's need to choke his lunch back down. The more he explored the more it dawned on him how everything had been converted to crystal. Not just the ponies, plants, or buildings, but also pollen and particulates that once drifted in the air were now crystal sand that had settled on everything.
The air was so clean that it had a level of sharpness to it befitting the new Crystal Empire. He had been given no reason to believe that anypony else had survived but he clung to hope. There were only two conceivable reasons for why he could have survived, either for his level of magical aptitude, or his familiarity with creation magic. He knew that the castle would hold the answer to which theory was correct.
A spire of pure jet stood where the sky-blue tourmaline castle once was. He slowly made his way up the onyx steps that led into the antechamber that, in turn, led into the throne-room.
It was the latter.
The ruling council had been addressing some topic of urgency at the time of the explosion as the Queen and all of her advisers had been gathered to court. As he strolled past the council members, the same twists of horror could be seen, and with them the same glassed-over lifeless eyes. It took him another minute to work up the courage to inspect the throne. The Queen had just enough time to pull her wings up over her face to deflect the incoming energy. Despite this she still ended up preserved in the black amber.
Something deep inside prompted him to get a better look at her face. After five years at her beck and call he had to know if she went out with fear or if she had been regal to the end. Sombra maneuvered to a position where he could peak through her feathers to see her face.
Rage.
A slow, condescending, clap echoed from the antechamber. The scrape of both hoof and claw could be heard on the polished crystal floor. "Bravo," the deep rich voice of Discord congratulated, "Now that is what I call a long game... for a pony." The draconequus went on to rub it in Sombra's face, "You won! Now you have all the wealth and power in the Crystal Empire."
That wasn't exactly how Sombra would have phrased it though. It was his fault. When he drew the sword, he broke the shield, and now had nothing left to fight Discord with; but it was more than that. There was simply nothing left.
No... That wasn't true. The structure of the crystal that the city was converted to was expressly designed to amplify Sombra's power, and now there was more than ever. His face sunk into a sullen stew as he reached out to the crystals the way that Treeling had shown him. He'd be damned if she was the only one that learned anything from their time together. Though, Discord seemed unconcerned as he gave himself a literal pat on the back.
"Though," Discord said, "I had really thought that Queeny would have gotten you before you got this far."
Sombra dug deep, building up the depths of his magic so thoroughly that his body was backed up all the way to his eyeballs. A green light shown from them as his pores radiated the vaporous shadow that would serve as his gilt. He wanted to curse Discord as he cast his prism prison spell, but there were no fitting words so instead he simply yelled in frustration.
While not the epicenter of the explosion, they were in the center of the city with focusing crystal on all sides, and Sombra brought the power of the entire city to bear against Discord. Such a graveyard would serve a fitting place to bury the world's enemy, and Sombra felt no pony would dare enter such wretched place so there would be no risk of Discord escaping again.
"Wait for it," Discord said as his body started to crystallize. The crystal crept up his legs then to his waste before he shown any signs of worry. "Uh, any time now..." he added.
Having a city sized focusing crystal was not the same as having the populous use Crystal Heart, but it was enough for a one shot entombment spell. The amount of power being channeled through it cracked the dome, causing the serrated sky to rain down on the city as the tower fell down around the trio.
"You did this!" the familiar voice of the Queen screamed from behind Sombra. It didn't matter that Discord was up to his neck in crystal. Her city had been destroyed, and her citizens annihilated by a traitor, all after she had harbored him for years. Death would be too good for him, and Sombra knew it.
With her connection to the Crystal Heart the Crystal Queen converted her still-raw emotions into a powerful magic that she lacked the horn to direct. White light beamed out from her core and radiated through her entire being. Her massive wings spread intimidatingly over him and she reared up with a bereaved wail. She brought her fore-hooves down with divine authority, crushing the floor of the chamber, which caused Sombra to fall as she stared him down from her throne. It would be a short drop since he wouldn't make it to the ground. As Sombra fell to the Crystal Heart a pyre of brilliant energy burned straight up into the sky.
In the embrace of lost love's light, he could feel himself burning into a shadow of his former self, and as his body cracked and broke apart when a voice called to him.
A child's pitiful cries could be heard behind sobbing tears.
***
Brittle bits of black crystal fell from the ceiling with some small shards bouncing off Sombra's head before clattering on the floor. The filly's cries could be heard coming from outside. He jerked out of his chair and collapsed on a pile of broken crystals. The entire room had been glassed over, but recently had begun flaking and melting back into shadow. Sombra tore through the room to look outside. Treeling was crying with her horn stuck into the trunk of a tree that she had pinned a squirrel to. Though she ran it through it was still alive, still squirming, and still scratching her face while she whined.
The darkness dissolved behind him and as he watched the filly squeal it hit him, she had just wanted to go play outside after a month of incarceration, and he shouldn't be surprised at the lengths she was willing to go to get what she wanted. After all, he was weaponizing a monster. He was still sweating from the experience but was able to breathe a little easier when he looked to the crowd that was gathering. They too were still alive.
He then realized something the he hadn't considered. She could combine magical energies. That and he needed to learn the perpetual image spell that she used on him. Since it came from his magic, it must be some combination of the mental projection, and the crystal empowerment spells.