Image imported from derpibooru 
Alt Link (Warning: May link to something unrelated) 
Original Description:
 
Twilight Velvet has a secret: she’s not a pony. Or a changeling, for that matter. No, she came from a far away place, a place that you could view from a distance at night. She had been a dream once, a nightmare, conjured up by Princess Luna in order to torment herself while she was trapped. The Tantabus had always been there, her guilt just as strong as Nightmare Moon. Velvet was a piece of that nightmare, of the Tantabus, until one evening during nightmare night. Nightmare Moon had been raging at her sister, able to view her through her minds eye, and saw her sadness and regret as insulting pity. During her tirade, a surge of magic sliced Velvet clean off, a fluke. Cut free, and not bound to the moon like her mother, she fell down to Equestria.
 
For the first few years, Velvet wasn’t even a person. She had no personality, no thoughts or feelings, just one basic instinct: to be a nightmare. So Velvet did as her nature told her, and hopped from vessel to vessel, tormenting their nights with their deepest, darkest regrets. One day, she had hopped to a new vessel, an older stallion wizard heading into the woods. He arrived at a deep, dark cave, where a small camp had been built. Inside was the first thing that ever really stirred Velvet.
 
A young stallion, but not a stallion. Paws and sharp teeth and claws, and bright red eyes. His fur was a dark blue, speckled and stained with the stars that reminded her of her home. She lept from the older stallion to him, and waited for nightfall.
 
Initially, Velvet did as her nature intended. She took over his dreams, filling them with horrors that no other pony she had encountered could withstand, but nothing seemed to effect him. Finally, she felt something… frustration. Why was this not working? Was he entirely different from the rest? Once she started to question herself, he became aware of her presence as well.
 
He introduced himself as Night Light, and tried to start a conversation. Considering she had never spoken before, she had a hard time trying to figure out what to say. It was kind of difficult to say anything when you didn’t have a body. So, in his dreamscape, she created a body for herself. A simple one, a black void with stars. The conversation was awkward at first, Velvet never having spoken before. But the more she did it, the easier it was.
 
He asked her if she had a name, but if she ever had one, she never knew it. She felt like her mother had named her something, but she had never spoke it, even in her dreams. He decided to name her Twilight, for her appearance of a night sky.
 
They stayed together, and after awhile, Night Light explained that he was a magical creation, just like Velvet was. His father was a powerful unicorn wizard, testing his abilities with illegal spells. Night Light himself was a highly illegal magical creature, a hybrid of the Ursa Major and a unicorn. His kind was practically unheard of unless you knew the right ponies. They bonded over their shared strangeness, both outcasts in such a magical world.
 
When Night Light told her he loved her, Velvet felt a… spark inside her. Something warm, and wonderful, that shone so brightly it bled through her heart and into her skin. She had been purified, no longer a nightmare, but a sweet, deep dream. The black void exploded into a bright white light that burned for only a second, until Velvet was finally there… not in the dream, but there, physically. She finally held her love in her own hooves, smiled with her own lips, and finally knew she was a real person at last.