Moon Dust and Black Night

One blackened night, a dark blue alicorn mare was running through the dark, enchanted forest known as Everfree. The mare was looking for the dark lair of "The Nightmare Pony". She had heard she can make you have your heart's greatest desires, but with a consequence. The mare wanted the ponies of Equestria to love the night, and so, she wandered into the Everfree Forest in search of her. She soon spotted a dark, twig & leaf made hut, with a purple glow coming from the door. The dark blue mare knocked on the door. And it opened. "Princess Luna?... Come in, my child~. You look like you need my...assistance, hmm?" The Nightmare Pony spoke softly, with a hint of slyness. "Are you The Nightmare Pony?" Luna asked. "Why, yes I am. My name is Moon Dust, your majesty." Moon Dust replied. "May I see you? I can't see you in this darkness." Luna asked. "Yes you can. But don't be afraid." Moon Dust hissed. Luna lit up her horn, to be greeted by a white pegasus with purple streak hair, and blue eyes, which had...smoke coming from it? "You...what are you?" Luna asked as she lit up the room with a dazzling moonlight. "I am a Magic Pegasus. Whenever I use my magic, I change form. I was born from a dark substance, from the forbidden lands of Tartarus. But, you're here for something, aren't you, Princess Luna?" Moon Dust looked at Princess Luna. "Yes, I am. I want my night to be loved and respected. I need...to be different. Big, like my sister, Celestia." Luna begged. "I can make that happen, little one." Moon Dust slyly said. "You can do that? But how?" Luna asked. "All I need to do...is take over you. "T-take over me? What do you mean by take over me?" Luna started to get tears in her eyes. "All I need to do is possess your body. It will be fine, you'll see. Trust me dear. I've helped many like you, and they've all turned out fine~." Moon Dust evilly grinned, her second form starting to show. "Fine, if that's what it takes, then do it." Luna crouched on the ground. Moon Dust changed into Black Night, and took over Luna's body. Luna let out a blood-curtling scream. And, then, for a slight moment, it was quiet. And then, a maniacal laughter erupted from the darkness. "I am no longer Princess Luna, but Nightmare Moon!" Nightmare Moon cackled, and flew into the night, heading for Celestia's castle.
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So, this is like a headcanon pony. She was the one that turned Luna evil, it's not what the storybook told you.
Base belongs to 6Sasu6Hina6 
Moon Dust & Black Night belong to me, MinkaExE