Chapters Luna (a purply-blue alicorn made with midnight blue mane and tail and turquiose blue eyes) was strolling through the palace gardens when she was teleported to a throne room. It looked like the crystal empire palace's throne room, but horribly twisted. The white pillars were black, the throne a staligmite of rock and the crystal walls, ceiling and floor were all rocky and burned.
"Wha...? Where am I?"
There was a cold chuckle from behind her.
Twirling around, Luna looked into the darkness. Then she cried out. "Sombra! I should have known." She narrowed her eyes.
His eyes streaming purple smoke, he walked forward to greet the princess. (Sombra had been the apprentice of starswirl the bearded before being corrupted by dark magic and turning himself into a unicorn. He used his new found powers to wreak havoc on the crystal empire and become the tyrant King Sombra.)
"Ah, Luna, so glad you're here."
"Why did you bring me?"
"To talk to you of course. I certainly can't just teleport myself to you, especially since you'd have you're powers. Oh, you didn't notice? Your powers don't work here, being of regular magic. Only dark magic works here."
"Make it quick. I've no patience for the likes of you." Luna said, trying not to convey the fear she felt inside to her voice.
"Maybe its time you got what was coming to you then!" Sombra snapped viciously.
"Oh, yes? And what would that be?" Luna smirked.
"THIS!" Sombra yelled
"Ah! Luna cried out in pain as her spine cracked against a pillar. Immediately, errant crystals (black crystals of very high value) grew around her, holding her in place.
Sombra chuckled. "Is that the best you can do? No wonder Discord found fighting you easy, didn't you Discord, my draconicus friend?"
A shadow rippled around the walls and entered the gilded crystal mirror to Luna's right.
"Yes, Sombra, I did find fighting her easy, even with her sister to fight also. They aren't very well trained, are they? I mean, over 1000 years old and still can't do a karate chop."
"You touch one hair on Celestina's mane and I swear, I will hunt you down and destroy you!" Luna raged.
Discord and Sombra looked at her, each with an eyebrow raised. They then turned to each other again.
"Very brave words for a powerless pony at our mercy. Still though, you have to admire the courage to rebel, even as foolhearty as it is." Discord commented.
Luna's body convulsed in pain as Sombra sent dark tendrils of magic into her, forcing them in deep. "I'll just change you to a filly, an Earth Pony, and take your powers."
"No..." Luna begged. Then she screamed, her unicorn horn shrinking, her pegasi wings shedding their feathers.
"Now your out of the way, its time to get our plans together! Hahaha!" Discord cackled.
"No..." Luna whispered again.
Luna screamed as her body began to bubble, jets of dark magic stabbing through her system, rattling her every breath. After several painful minutes, the ordeal was over. She was now a little Earth Pony filly, weak and helpless. The fear in her tearfilled eyes was plain to see. Discord and Sombra were laughing cruelly at the princess, mocking her mercilessly. Discord wiped a tear from his eye. "Ah, Luna, Luna, Luna. You always were fun to torture."
Luna cried as Sombra drove dark magic needles into her, his mouth twisted into a painful grimace. "Where is your sister, Luna? You should tell her to watch out, I'm coming for her! Hahahahaha!" he said in a fit of insanity, laughing maniacally.
Luna teared up again. She felt saddened. She had lost her friend to a terrible fate. "Please, Sombra, dont hurt her. Sombra! Please! Listen to me! You arent thinking straight! The dark magic is causing your insanity! I can reverse some of the damage but-"
Sombra cackled. "Do you really think I want you to fix me? Youre stupider than I thought. You betrayed me! You tried to stop me forfilling my dreams! You aren't my friend. You're my arch enemy!" He shouted the last part. Then his voice dropped to a whisper. "I'm going to love destroying you, Luna." He then drove his dark magic in to her and, after shouting a triumphant cry, he witydrew his magic and the made blacked out, her figure marred only by her eyes... Those scarred, terrifying eyes...
The filly woke. Strange dreams of giant shadows and draconici haunted her. But the shadow... It looked like the shadow had just stepped out her dream. The shadow looked at the filly. Then, it struck. The screams echoed... Forever... The cavern disapeared...
"Ah! Wha... Where am I?" Luna panicked. Then she recognised her room, her stuff, her... Nightmare Moon doll? She didn't have a Nightmare Moon doll. Then she streched, and in doing so, realized she was still a filly...
Her sister came bursting in. Raised her horn. "Wait! Sister, please!" Luna cried.
"Luna?!?!?! Is... Is that really you?!?!?!
Bonus Chapter - what happened to Celestia
Celestial looked at the time. It was sunset. Time for her to lower the sun. But, wait... "Something isn't right." She murmered. "Where is Luna, and the moon?" Her guards didnt know, so she went to ask her sister's guards. But they didn't know either. Celestial was worried. She ran to her sister's room. Lying on her bed was a little Earth Pony filly - clutching a Nightmare Moon doll... Celestial raised her horn... "Wait, sister, please!" The filly cried.
"Luna! Is that really you?"