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Original Description:

Midnight blue hooves slammed on the pure white marbled floor harshly enough to manage to shatter it into segments. The cracks formed a split all the way to her sister, guiding Luna’s tearful gaze to reveal how truly shocked Celestia was. “Why are you acting like a spoiled brat Luna?!” The almighty alicorn repositioned herself to stand tall and superior to her sister as she always have. Luna, easily offended by this act, screamed hysterically at her with desperation to be understood for once. “…YOU WERE NEVER THERE FOR ME! WHY CAN’T YOU JUST SEE THAT CELESTIA?!” As always, Celestia showed no signs of empathy for her little sister. “LUNA! Knock it off with your jealousy already! I can’t always be there for you. I have an empire to run!” Celestia snapped back. Luna’s face dropped with an intense hurt. Then her face regrew into a snarl. “I… I HATE YOU!” Luna refused to hesitate to spit out, absolutely enraged and hopeless. Before Celestia got a stern hoof closer, Luna used her power to launch Celestia out of her room with such force. Quickly, she slammed the doors before getting a good glimpse of Celestia slamming against the wall firmly.
Luna slumped down sitting and hiccup-crying for an hour. That is, until she fell asleep on the cold flooring below.

“…Where in equestrian am I?” The sobbing mare with a hoarse voice hiccupped out. Luna stood with her knees wobbling slightly. Some how she was suddenly standing on clouds in an enchanting new moon-lit world. This was indeed her style. “Oh. This must be a dream! Thank Equestria! Some peace away from my snobby, stuck-up, show off-y, sister.” Luna said to herself, a breath of relief audible. Luna’s shadow grew elongated as the moon towered over Luna. A hauntingly-beautiful mare formed from out Luna’s shadow, the mare now standing before Luna. A grin twisted in the strange mares face. “What if I can make your… Ahem… snobby, stuck-up, show off-y sister… Go away for good?” The mare spoke out in a somewhat soothing voice. Luna stumbled back in shock as she was beheld of her much more mightier form of herself. But soon she realized she wanted to be MUCH more the mare her sister ever was. Mare, Nightmare Moon…

A small tale inspired by one of the My Little Pony fandoms biggest hits - Lullaby for a Princess