1,000 years ago in the great kingdom of Equestria there were two Alicorn princesses Celestia and Luna, Celestia made the sun rise and fall, Luna did the same with the moon. They both ruled over Equestria equally and Equestria was living in a time of peace and harmony under these two princesses who held the great Elements of Harmony that they had already used to defeat Discord and then King Sombra.
Unfortunately, Things were not as harmonious between the two sisters. Princess Celestia had been beloved by one and all. This had caused Luna to feel left out. She never mentioned these feelings though.
This morning, Celestia had just brought up the sun and started a new day as the ponies everywhere all woke up from their slumbers of sweet dreams that were overseen by Princess Luna. The ponies would wake up to see the shining beautiful sun brought up by Princess Celestia who was loved by all.
Today Luna had just put the moon back down and Celestia has pulled up the sun. She felt sad inside that ponies didn't seem to appreciate her night as they would often sleep through most of it. She would feel quite saddened by these thoughts but she could never bring herself to blame Celestia her older sister who she loved with all her heart.
Luna was walking through the palace. She saw her elder sister trotting by, Celestia noticed Luna who meekly waved. Luna's sister beamed at her.
"Hello Luna I'm going off to greet the citizens today you can take care of things here right?" Celestia said with a smile.
Luna smiled, nodding "Of course."
Her sister then hugged her and said "I don't know what I would do without you."
Celestia flew off as Luna waved goodbye. Luna decided to go off to the library and she walked passed two guards who bowed to her and Luna said "Thank thee thou my rise."
She liked using her "royal" accent. It was a fun thing for her to do, she needed small things like that. They helped her through the day.
Eventually she entered the library and found a book and began to read it. Sometimes, she did not mind being alone. At least it gave her time to herself.
Soon enough, she felt a cold feeling in the air. A feeling of dread was filling her stomach. Luna did not know why she was feeling this way.
"Luna~......" A demonic voice was heard.
The Moon Princess felt a chill from within, she set her book down. There was a silence, Luna looked around. She was the only pony in the library. No one was there, she continued to read.
"Luna~...." The voice spoke again.
She felt panic from within her, she put the book down firmly. She looked around nopony was there. She was feeling scared now.
"Whoever thou are, I command thee to show thyself!!" She exclaimed, hoping to sound confident.
A voice merely chuckled, the princess looked around. She felt herself panicking. The Princess had a hard time keeping it together.
"Poor Luna..." The Voice responded "It hurts, doesn't it. All of the loneliness and pain that you feel."
"Who said that?!!" She snapped "SHOW YOURSELF!!"
Her fear was evident in her tone. She had tried to hide it. Though she knew she was failing to do so.
"Don't be afraid my dear princess..." The voice spoke "I am here to help you."
"Help me?" Though still scared, she sounded curious "How?"
"You're jealous aren't you? Of your sister.."
"No! Of course not!" Luna replied defensively.
The voice said "Yes you are my dear foal you are, your sister is so beloved and celebrated while you're not it must be horrible Luna."
Luna looked down and stood silent. This being's words spoke true, deep into her heart. She could not deny his words. As they were on her mind, so many nights.
She said "Yes, it is so unfair...."
She looked down, letting out a sob. The feelings were starting to come out of her. It was so painful.
The voice spoke, sounding more sinister "Yes it is my dear and I can help you get your revenge."
Luna's eyes widened "Revenge??! She's my sister I could never hurt her!"
Soon she saw shadows covering the room as the voice said "You can and you will my dear."
"STOP THIS DEMON!" Luna shouted, attempting to sound brave.
She felt a coldness throughout her body and said timidly "Please...please..stop...please stop.."
The voice chuckled darkly and said "You fear me good... I knew you did"
Then a big blue eye with a black slitted pupil appeared and Luna screamed horrified beyond words as all of her worst fears pains and memories and nightmares surfaced.
Then another eye appeared and fangs appeared as Luna was frozen in abject fear as she saw the massive horrific creature infront of her an he said "I am the Nightmare and you will work for me and follow my desires and in return I will help you accomplish your goals and you will be mine Nightmare Moon."
Dark smoke entered Luna's eyes and they changed shape briefly and changed back as she bowed to him. She felt different now, she couldn't explain it. Evil thoughts were flowing through her.
Then Luna found that she was in the library again. She looked around, noticing total emptiness around her. No sounds could be heard.
The princess smirked "He was right I will have my revenge against Celestia my treacherous unloving sister she's been using me all along that traitor."
Hours went by, then Celestia returned and said "Luna I'm back."
She heard no response and said "Luna..?"
Luna stepped out of the shadows and said "Hello sister."
She smiled, an eerie smile. One filled with malevolence and evil. This made Celestia shudder, she had never seen Luna like this before.
Celestia said "Hello Luna sorry that I came back late it's time for me to pull the sun down so it's time for you to raise the moon."
Luna said "Of course sister."
Celestia then went to bring the sun down as Luna grinned.
Luna said "Foolish sister soon you will fall before me."
Then when Celestia came back Luna lifted the moon and then she grinned when she was finished. At dinner Celestia said "Luna you look very happy this evening." Luna said "Yes sister I am feeling quite happy."
Celestia said "That's good to hear."
A few hours later they both went to bed. That night outside of Luna's door dark smoke issued forth into sleeping guards who screamed in horrific pain and dropped dead on the floor. Celestia didn't hear this at all as the Nightmare kept her from hearing it as he plagued her mind with horrific nightmares and bad memories and her worst fears Celestia was in tears and couldn't make herself wake up.
That night The Nightmare caused ponies horrific nightmares for several hours. Then soon Celestia woke up late and she she made the sun rise and then she senses a disturbance in the
She runs to the throne room and sees dead bodies in the halls and then is in the throne room and hears Luna say "Not another step." Luna then steps out from behind her throne. Luna glares and said "Did you really expect me to stand idly by while they just basked in your precious light." Luna stepped in between the thrones by the railing and said "There can only be one princess in Equestria and that princess is.." Her eyes glow as she bashes the ground "ME!" she causes damage as shadows appear and the window behind her breaks as the moon rises and covers the sun.
Shadows envelop a surprsied Luna as she rises into the air and a ball of orange light glows as she then appears transformed into he Nightmare Moon form as she laughs madly. Celestia looks at her in shock and horror.
Nightmare Moon blasts around the ceiling showing the moon as Celestia glares downward thinking "Luna...What are you doing."
Everypony was in panic as they saw the moon was up. One colt said "Mama I'm scared." The mother held her foal close.
Nightmare Moon stepped closer to Celestia as the palace was damaged. Celestia glared and said "Luna it is your duty to raise the moon."
Luna said "Luna? I'm Nightmare Moon! And the night will last FOREVER!"
Celestia glared and said "I will stop you!" She blasts at Nightmare Moon with her horn and Nightmare Moon dodges it and blasts Celestia knocking her back and then their battle continued as they damaged the castle and Nightmare Moon blasted Celestia knocking her down and unconcsious.
Celestia struggled to get up as Nightmare Moon laughed. Celestia got up and summoned the Elements and she blasted Nightmare Moon with tears in her eyes and she thought to herself "Please forgive me." She blasted Nightmare Moon who was screaming into the moon as a shape formed into it. Celestia then lowered the moon and the sun appeared.
Everypony cheered as they all cheered the name of Princess Celestia. The first Sun Celebration began and Celestia made a new castle in Canterlot as the original one was damaged beyond repair. Celestia put up a brave face for her subjects but her heart was broken by what had happened.
In private she would cry silently and say "Luna it's all my fault I should've treated you better and now you're gone."
Little did she know that The Dreaded Nightmare is behind all this and he's content in that he ruined some lives. Nightmare laughs as he has won and a few days later he killed 100 ponies in their sleep for fun. The Nightmare is a truly horrific creature who can damage or corrupt any creature or anything.