"S..Sombra?!" sputtered Twilight.
One you have already faced.
"Yes, Twilight. Sombra was... a unicorn, talented and powerful, known as Dawnstar. He did not always seek the power and control that he hungered for in the Crystal Empire. He was... ambassador there, once, but he chose a new path, one of domination and tyranny. He set aside his old name and took one of shadow when he seized his crown."
"But what would cause him to do this?"
"I cannot say more than this, Twilight."
She will not provide the answers you need.
"But you know more!" Twilight almost stamped a hoof.
"Yes, Twilight, but please. You will know all you must know in time, you must trust me in this. There are dangers in knowing even this much! I have guided you in your studies and watched you develop your friendships. I have tested you... "
I have fought, but failed...
"... but only when I judged you ready and able to succeed."
"It's just... if you are sure that Sombra was defeated, then we still don't know what caused the accident. It's so... close to what he's done before, but even in my dream, it was not quite... "
"Dream?" Celestia's head snapped towards Twilight, the Princess' eyes ablaze. But also... afraid? "Twilight, what dream? I asked you to tell me of anything unusual."
"I'm sorry, Princess. It... I dreamed of that crystal... "
It marks the beginning.
"Twilight, this - "
A massive quake rocked the balcony, interrupting the conversation, throwing Twilight to the floor, and knocking the Princess against the railing. The echoing noise of cracking stone and shifting earth resounded in Twilight's ears as she lay there, stunned. The Princess braced herself against the balcony's edge, a soft glow from her horn appearing to encase the pair in a magical shield, just before another quake shook the floor again.
"It's another one! Another crystal!" shouted Twilight above the rumbling as she struggled to her hooves.
"No natural earthquake could strike here!" yelled Celestia in agreement. Alarm bells from Canterlot began ringing, and the distant shouts of citizenry added to the pandemonium of noise started by the quake. "We need to find Princess Luna, Twilight!"
"Luna? But - "
"Canterlot can handle a quake - it is you who are in danger!"
They could not move, however, as continued rumblings left them shaking and barely steady behind Celestia's protective shield. With a sharp crack, a line appeared in the floor from the doorway to the balcony's edge, leading straight under Twilight's hooves. She saw the danger immediately.
"The balcony's breaking apart!" she cried. Another quake stumbled the two ponies and lengthened the break; now the crack had split and sent itself halfway up a nearby wall. "We have to get out of here!"
"Agreed!"
Princess Celestia focused her magic intently, boosting her voice until it matched the quake in intensity.
"Citizens of Canterlot! Abandon the Castle! Get yourselves to the safety of the city! The Castle is under attack - evacuate it immediately!" Her voice spread from the ledge, drowning out all other sounds, though she had thoughtfully used a muffling charm on Twilight. "Twilight," she said, her voice lowered back to normal, "On my back." The Princess lowered her hind legs, spreading her white pegasus wings wide.
Between quakes, Twilight, assisted by the protective spell, managed to ease herself onto the Princess' back, wrapping her front hooves about Celestia's shoulders. The Princess flapped her large wings, lifting them both into the air with a rush of wind. The magic bubble moved with the duo.
As Twilight watched in horror, the entire balcony shifted, and the huge crack split wide open, now running the entire length of the wall. With a great creak and groan, the mortar and bricks gave way to the strain, and the ledgeward side of the crack broke apart. The flowery metal design of the railway was torn in half as several tons of balcony, where they had just been standing, fell to the plains below.
Celestia flew further up and further out, and soon Twilight could see the rest of the castle. The whole thing was tilted, as if the ground had sunk on one side, but she could see the reason why. In a semi-circle twining around the castle between it and the rest of the city, dozens of towering black crystals had sprung up, cracking the ground, tearing up streets, and destroying adjoining buildings. Scattered ponies in uniforms and guard's armor rushed out from the castle, dodging between the black towers wherever they could to escape the castle grounds. Celestia rushed herself and Twilight towards the city beyond the menacing ring.
Dozens of the royal guards, including the Captain, were gathered in a tree-lined street beyond the crystals, where Celestia landed. Twilight hopped down, and the Princess folded up her wings. Maids, librarians, cooks, and other dwellers of the castle continued to stream through the narrow passages made by the crystal obstructions.
"Twilight, don't go anywhere," the Princess ordered. Twilight nodded meekly, and the Princess, pausing for a moment to see she was obeyed, turned to the Captain.
"Captain! Form squads - I want every guard, servant, and visitor to the castle found, accounted for, and taken to safety!"
"Yes, Princess!" the Captain saluted with his right hoof.
Twilight looked at the row of crystals. The deep, obsidian surface shimmered back at her. Something glimmered...
There was another boom that sounded, yet this one came from the sky, not the earth. Twilight and most of the other ponies turned to see a rainbow streaking head-on towards the castle. Within seconds, Rainbow Dash had appeared, slowing from dizzying speeds to alight on the cobblestone street next to Twilight.
"Twilight... " the pegasus called out excitedly between huge puffs of breath. "What in the... hoof is going on?! The whole town shook, I... took to the air and saw the castle... slipping! I told the others, they're coming!"
"It's some sort of attack, but we don't know what for!" Twilight responded as they looked at the ring of crystals.
"You just... " Rainbow huffed, "Point me to what needs to be done!"
"Rainbow Dash," said Celestia. She pointed to the Captain. "Please assist the guards in finding anyone stranded or trapped at the castle."
"You got it, Princess!"
Dash, the Captain, and the other pegasi amongst the royal guard took flight, speeding over the crest of crystal towers and heading back to the castle grounds to search for ponies.
No more crystals had appeared; the quakes had stopped and the rumbling diminished. The castle refugees were lining up into groups, most of them shaking or trembling, a few of them sitting or lying in the street.
Twilight, at Celestia's beckon, joined the Princess and the two ponies moved closer to one of the crystals.
"If this is a strike against us, I do not see its purpose beyond mere surprise and disarray," said Celestia, shaking her head and sending waves rippling through her mane.
Twilight moved closer to the glossy black surface. As in the dream, hundreds of reflections of her face appeared in the many planes of the tower, seeming to taunt her with twisted expressions that were somehow... off.
"Twilight, we need to find Luna, but... explain to me what it is that you dreamed."
The purple unicorn turned away from the reflections and looked into the eyes of her longtime mentor. She looked back at the tower, and a thousand eyes looked her way.
"I saw... one of these crystals... " One of these? Or this one? Did it not look just like this one? She looked to the left along the ring of towers, then the right, and gasped. All of the crystals were alike, exact duplicates, down to every outcropping, every shimmering surface where Twilight after Twilight showed shock and awe to mirror her own.
"I came near, looking at the reflections it showed. I thought I was dreaming; I knew it had to be so, and I decided to wake up, but even when I focused, I couldn't manage it. I got so frustrated, and I turned and kicked it, then it... "
Crack.