When I reached the Crystal Empire, what I saw was bad, something that I could never imagine. The city was a wreck, ponies that were everywhere before, now they just disappeared. I found a pony running away, but he didn't went very far away before getting caught in a magical aura and getting pulled back to the mine area, I could only ask him a question. "What happened here?"

He could only whisper a word. "...Sombra..." Before I could ask him more questions he was pulled back on the mine.

Sombra, what is that? Is this a name? I never heard it before. I think I will discover soon enough. With this, I headed to the mine.

Sombra was inspecting the ponies that were mining, he noticed that one pony tried to escape, but he didn't went far away. He knew that somepony entered the city and now was in the mine, but he didn't know who it was. His questions were about to be answered.

With this, my presence was revealed, my jaw went to the ground, I couldn't have possibly expect what I saw. Who is him, he looks like Shadow, but it's impossible for him to be.

Sombra just laughed madly, his laughter echoing through the entire cave. "HAHAHAHAHAHAHA... Luna..."

He knows me? I never saw him before. "You, who are you? How do you know me?"

"...Crystals..." Was the only response that I heard.

"Tell me, who are you?"

"Sombra..." He said before starting to growl.

"So, you are Sombra, what do you think you are doing with the ponies of this empire?"

"Slaves...Crystals..." Was the only thing that left his mouth.

"This is your plan, turn them in slaves?" But silence was the only answer. It can't be, the color of the fur, mane and tail, the style, it's the same, just the mane is a little different. The same eyes, but now with a purple stream of magic coming out from them, I can't believe it, it's him! "Shadow, is that you?" I tried to ask, but only silence answered. What is wrong with him, he can't speak normally?

With this opening he went to the attack, he sent dark crystals in my direction, I couldn't believe, was Shadow attacking me? I tried a shield spell, it worked, but the shield shattered to pieces, crystals are really hard to break, but the shield stopped them.

He tried again, failing. I, noticing that he wouldn't stop this madness, got out of the mine and escaped the Crystal Empire with tears in my eyes.

With my jealousy already taking the front of my thoughts, I couldn't stand with the shock of losing Shadow, these factors together pushed my mind at the limits, I couldn't stand anymore, I gave in to darkness, I turned to the form that even today haunts my dreams, Nightmare Moon.

Sensing that I was going to the castle, Sombra thought that I told my sister of this and we were preparing the Elements of Harmony to use against him, he knew about them, they were the only thing that could stop him now, sensing this danger, he put a curse in the Crystal Empire, and then, locked the empire magically for a thousand years.

Author's Note

Knowing that Nightmare Moon appeared first a thousand years ago and the Crystal Empire was cursed in the same time, I put two and two together and came with this theory, this was rather difficult to build up, sorry if things look strange in this theory, but is the best one that I can think of, say if you like it and tell me if you think that something is wrong here, you are free to criticize the way you want.