One thousand years ago, after the Siren's were banished to the world beyond, the Crystal Mirror was taken to the more fortified Crystal Kingdom. Every generation, a new guardian from the greatest of the Crystal Army would be appointed to guard the mirror should they ever return. Swearing in secrecy, only the first guardian knew of this purpose. Years went by and each succeeding guardian would know nothing of what they were guarding, nor could see it. One guardian would break that oath.
Sombra or the pony that would be known as such was first found in the frozen wilderness of the Crystal Kingdom. When he was brought into the orphanage, Sombra had very little words to speak, most often his own name. This slight learning disability, along with being "mark-less," made him an easy target for teasing. One day, another young pony by the name Radiant Hope is brought in the orphanage. Noticing the teasing she's been receiving, the two have been very close friends. While Radiant Hope's body became more crystalline like the inhabitants around her, Sombra remained the same, though he felt the aches and pains. Feeling sorry for him, Radiant applied her healing magic to him, unintentionally receiving her cutie mark in the process.
Noticing her potential, The Royal Sisters took Radiant under their tutelage. Sombra, now alone and still without a Cutie Mark, decided to find his place in the Crystal Army. With none of his former orphan mates around to tease him, Sombra trained and fought hard against the Windigoes that once threatened Equestria. Noticing this great deal of courage, Princess Amore took him in and anointed him as Guardian. Sombra couldn't be any happier, he was away from the ponies who teased and taunted him while being part of the Crystal Kingdom's alumni. What more could be done to impress Radiant Hope when she returned?
Years pass and Sombra has yet to receive word from his good friend. The aches still happen, but not as much from when he was young. For a long time, he stood guard, not moving one muscle unless it is to pay respects to the passing Princess Amore or a thief would try to steal a prized object nearby. One day, one of the passing alumni stopped and looked at Sombra as he stared into the horizon.
"Hmph!" - Chrysalis walked over to the Guardian - "Ever since as a little filly, it never fails to amuse me how the last guardian just stood there."
Sombra, either out of duty or to shrug off her annoyance, ignored her and continued his watch.
"Do you even know what you're guarding?" Chrysalis added
"I am sworn to secrecy not to disclose what is behind the doors." Sombra finally answered.
"Yes, but you know just what you're guarding?" - Sombra's silence frustrated her - "And to think" - She begins stroking the stallion's arm - "you, all alone in this hallway" - Chrysalis slowly reaches up to his ear - "unloved..."
Chrysalis' ears flicked to the hum of magic.
"Leave, now..." Sombra growled as his horn glowed.
Chrysalis stepped back to her level and began walking alway.
"Even good deed's never go unpunished." She hissed as she left the Guardian's sight.
Annoyed as he is, the brief conversation did spark some debate into his mind well into the following night. Sombra growled as he fought his away his curiosity. Then there are the memories of him being called "slow" or "not up to speed." For the first time in years, Sombra snapped out of his mind, turned around and slowly opened the door.
Inside were a series of knick knacks; ancient robes, tapestries, and jewels from the former rulers of the Empire lined up along the shelves. The large Unicorn looked around and found his answer. The Crystal Mirror, as fine as it stood years ago, was right in front of him. Sombra raised an eyebrow as he approached the mirror.
"What form of sorcery would this worthless object have?"
When he looked at his reflection, Sombra was unamused. But when he noticed something happening to his reflection, the Guardian looked harder. His reflection aged back to when he was a colt, and even further as just mere shadow seeping into a red crystal. He was then shown his adult self again exploding into several pieces by the power of one object: The Crystal Heart.
He stumbled out of the room, his eyes smaller than they were before. Now there were so many questions: What was he? What's his purpose?
Sombra raced down the hall, past the night guards and to the chamber of the Crystal Heart. As it is still night, the room was illuminated a soft blue from the Crystal Heart. Sombra slowly approached the relic, wincing in pain as he got closer. When he was six inches away, his body began to crack. Not wanted to risk oblivion, he stepped back, noticing the blue cracks receding.
When he got back, Sombra found Chrysalis along with a few guards standing next to her. His intentions revealed, Sombra growled at her as she curled her lips into a toothy grin.
The next morning, he was brought over to the throne room, where Princess Amore waited. The ruler kept a gentle glare as Sombra knelt before her.
"Sombra, when I anointed you as Guardian you swore of secrecy. Am I correct?"
"Yes, your Majesty." Sombra turned his eyes over to the smug Chrysalis.
"You understand the consequences of breaking that oath?"
"Yes, your majesty." Sombra raised his head up "But my questions need to be answered: What am I, and why does it hurt to be near the Crystal Heart?"
The Crystal Princess closed her eyes - "You, are an Umbrum, a shadow pony."
Sombra was taken aback, "How can that be? I still walk among you."
"Some can manifest themselves into a physical form. Only by the power of the Crystal Heart shall they be destroyed."
When Amore opened her eyes, she found Sombra's eyes closed shut.
"In light of that," - Amore rose from her throne - "I have decided that you should be banished from the Crystal Empire." - She approaches him. "The mirror only tells of what may happen: you still have the power to change."
As she places a hoof on him, Sombra's eyes shoot open. Dark energy flowed outwards as his body lost it's physical form and became shadow. Outside the kingdom, the darkness blotted the sun, bringing concern to the Crystal Ponies.
"Seize him!" -Chrysalis ordered- "Protect the Princess with your life!"
Without even turning around, Sombra's dark magic made the surrounding chamber from a glacier-blue to an obsidian-black. Red lines drew out the forms of ponies, which then broke out of the walls and began attacking the guards. Without much effort, over half of the army became overwhelmed by him. Sombra continued to stare as Amore as his crystal soldiers held his prisoners.
"What shall it be, Princess?" - Sombra wrapped Chrysalis in a veil of darkness - "Your throne or your subjects?"
Princess Amore stood tall, merely glaring at the Shadow Pony. Sombra took that as his answer before focusing on Chrysalis.
"In my time as Guardian, I have heard much about you from the Castle Guards. Your lust has made them fight for your love." Sombra narrowed his predatory eyes, bringing more fear from the Unicorn - "They view you as a princess, so I shall make you and your admirers as I see in you. From love they fed upon, and so love you shall feed as well."
The shadows swallowed Chrysalis and the captured soldiers. Amore shut her eyes as they screamed in their transformation, all the while the Shadow Pony gave a toothy grin.
Suddenly, Sombra felt a sharp pain inside him. He turned and found Princess Amore with her horn lit. Outside, the Crystal Heart was in motion as it was lowered to the centerpiece just below the Palace. Sombra's body became physical again, releasing his prisoners. Blue streaks began lining up on around his body. Amore kept at her magic, not backing down for one second. Sombra, in one desperate attempt to save his life, used a surge of black magic to become shadow again and wrapped around the Unicorn.
A short scream.
Then silence.
Sombra returned to a physical manifestation, now with red eyes and his horn curved slightly and having a pigment change from black to blood red.
Chrysalis woke up to find unrecognizable beings. They were charcoal black with blue carapaces and chitinous legs and wings. When she looked at the floor, her visage was horrifying. She had the same features as the others, but also her "mane" and "tail" now has the appearance of a spider web, a mere shadow of her once beautiful mane. She looked not only to find Sombra but also Princess Amore, now a crystalline statue.
"Farewell, my former master." Sombra closed his eyes when his ear flicked to the sound of magic. In a quick evasion of shadows, he dodged the green blast, destroying the statue in the process.
Chrysalis placed both of her "hooves" at her mouth as Sombra appeared behind her.
"You brought this yourself." He whispered in her ear.
Sombra stepped over the pieces of the now deceased Princess and sat on the throne. Chrysalis hissed at him as the other abominations awoke.
"Leave my kingdom" - Sombra growled - "And never return."
"One day, I will have your head!" Chrysalis shrieked at him before being shoved by a crystal soldier.
Defeated, but not willing to give up, Chrysalis wrote a letter to the Royal Sisters.
My Fair Rulers,
I bring with a heavy heart that Princess Amore was killed. Slain at the hand of the Umbrum known as Sombra. He has taken the throne in her place and now rules the Crystal Empire with an Iron Fist. Please respond immediately to this crisis.
Your faithful subject.
Upon being read, the scroll was dropped onto the floor. Tears dripped on the letter as we see the last free Crystal Pony Radiant Hope weeping.
"Sombra..."