Me: So, I was really bored and I wanted to test my hand at MLP. I started to watch FIM and I was fascinated with the Mare in the Moon arc. There was along that I wanted to explore and play with and this is basically my theory as to how Nightmare moon came to be. Out of all the villains, Nightmare Moon and Discord are my favorites and Nightmare moon is kinda under explored. Hence the magic of Fanfiction! :D Anyways, I don't own any of the characters. I may or may not add an OC. We will see. ;) Enjoy!

Celestia smiled as the setting sun painted the sky vibrant orange, gold, pink and purple as it touched the horizon. The alicorn mare smiled as another alicorn, this one smaller with a dark gray coat and a blue mane trotted up next to her.

"You ready to bring out the moon, Luna?" She asked and Luna grinned, nodding.

"I was born ready!" Luna stretched her wings and hopped off the balcony, hovering not far from it.

"Don't lift it too fast, Luna." Luna frowned.

"Tia, I'm not a foul, I can do this." Celestia allowed herself a light chuckle at her sister's expense.

"Alright, but be careful."

"I will." Celestia then watched as the smaller mare took the skies, lighting her horn a soft blue glow. Luna felt so free as she flew. She loved the feel of the wind in her mane and tail as she coaxed the moon from its slumber. When the moon was in its place, Luna settled on a fluffy cloud and admired her work with a smile.

"Oh what the most lovely of nights." She muttered happily. She was about to fly back to Canterlot palace when she heard a voice.

"Princess Luna..." Luna looked to see a form of a stallion on his back legs.

"Who is there?!" Luna scanned the sky as the voice gave an amused chuckle.

"I am the darkness that lurks in the shadows of the night. I have seen that you have bitterness in your heart. All because you and your night is so very unappreciated." Luna frowned as a dark blue smoke took form of a tall alicorn mare that looked like her. Only this mare was black with a long flowing mane that seemed to be made of the stars.

"What are you?" The mare grinned evilly, showing the smaller pony her sharp fangs.

"I am the darker half, born of your hatred and bitterness. What do you say little Luna? Will you let me show the ponies the wonder of our dark jeweled sky?" Luna bowed her head and the mare lifted her chin with her ever-flowing mane.

"Don't you wish to get back at your sister?"

"No, Tia loves me for me, and the subjects adore my night." The mare growled.

"Fine, if you insist." Pain was all Luna could feel as the smoke wrapped tightly around her and squeezed. Luna let out a scream as the dark mare took hold of her and pressed her will down. Luna yelped as she was pushed into a far corner of her mind and she heard the mare laugh.

"Your sister will be surprised to see what you have become, Princess Luna."

"What are you doing? Leave Tia alone!" The mare laughed at Luna's pathetic attempt to be brave.

"Oh, you will see, Little Luna. You shall see." Luna could only see darkness. Her only window to the outside being a thin mirror like window to see though the mare's eyes. Luna bowed her head as tears fell on the black marble floor of her prison.

"I'm sorry, Tia. This isn't me, if I am the moon, then this dark being that has taken control is Nightmare moon..."

Nightmare moon had heard the Princess' words in her mind as she flew back to the castle.

'Nightmare moon? Hmm, I like that name, how fitting.' She grinned as she landed on the balcony. When she had taken over Luna, her coat had shifted from dark gray to black like a starless night with a splash of purple on her flank to make her now blue cutie mark more prominent. On her feet were tall boots and on her head and down her neck was a helmet of blue sliver.

"I'm back, sister." She called in Luna's voice. In the corner of her mind, she felt waves of angry echo off the Princess and Nightmare moon grinned. How she enjoyed watching her host struggle vainly. Princess Celestia stepped out and her eyes widened at the sight of her sister, who was now a mare she did not recognize.

"L-Luna? Is that you?" Nightmare moon chuckled, enjoying Celestia's shock and fear as to what her sister had become.

"Not anymore, Celestia. I am now Nightmare moon, and the time of your days have ended." It took a moment for Celestia to get over her shock.

"How? What have you done with my sister?!" She demanded and Nightmare moon chuckled.

"Oh, you should have seen the look on your face. It was priceless."

"Answer me!" Nightmare moon didn't flinch by Celestia's loud voice.

"Don't worry, I just made some changes to your sister."

"What do you mean?" Nightmare moon grinned.

"You didn't know, did you? That your sister was unhappy."

"What are talking about?" She chuckled.

"So they say that ignorance is bliss. Luna was bitter, everypony played in the day that you brought to this land, while they locked themselves away to shun the beautiful moon when shadows fell."

"That's not true. Everypony loves Luna." Nightmare moon snorted.

"Please, but you wouldn't matter now. Now everypony will know the wonder and beauty of the darkness. Night shall last forever!" Nightmare moon laughed as her mane and tail blanketed the sky in a twister. Celestia opened her wings and fired a beam of her magic at the other alicorn, but it wasn't enough. Nightmare moon frowned and used her own magic to send Celestia flying back into a wall. Celestia groaned as she shakily stood.

"So long, Celestia!" Nightmare moon's laughter echoed as Celestia flew from the castle. Her heart was heavy knowing that her sister had become a wicked mare of darkness. She had seemed so happy. Celestia didn't have a choice. She had to get to them. She had to get to the Elements of Harmony.