...Wake...
A horned mare with a dark blue coat slept in her lush bed. Her mane rested gently up on the pillow under her head, its texture appearing as a star-covered canopy against the dark night's sky.
"...You...it's...you..." she muttered, speaking subconsciously.
...Wake, my pawn...
The mare rolled over and her large wings unfurled from beneath the sheets. The mare was the Equestrian alicorn princess of the night, Princess Luna.
"...I...I am not your...slave..." she continued to argue with her own unconscious mind.
...Your mind belongs to me. I am the source of your power and your motivation. You tried to deny me but there is no true escape. Give in and accept reality.
Luna began to sweat profusely, clearly afraid of what dwelled within her dreams. She rolled over once more to try to fight off whatever was plaguing her.
"...Twilight...defeated you. She destroyed that part of...my magic!" Luna said, now more clearly and gradually beginning to gain consciousness. She gritted her teeth, as though she were trying to force her subconscious mind to repel the unwanted thoughts.
It is futile! There is no choice; I will reclaim what Twilight Sparkle has cost me and you will do my bidding!
"NO!" Luna shouted, sitting straight up in bed, now fully awakened by her rejection of her dream. However as soon as she rose to full consciousness, a shadowy black energy began to seep out from behind her eye. "S-stop!" she cried, closing her eyes tightly and trying her best to regain control. "I...I...can't...AAAAAHHH!!!"
Within the laboratory of Star Swirl the Bearded the great unicorn sorcerer was indulged in an experiment. He levitated a beaker to his eye and sloshed the fluid inside.
"Hm..." he mused. "Perhaps a different ratio..." he said to himself. The beaker gradually lowered onto a table and was released from the magical power that grasped it. He levitated a pencil from within the pocket of his star-patterned robes using his unicorn horn and began jotting down some notes about his observations on a nearby tablet.
Before he was able to modify his chemical concoction, the wooden doors to his laboratory burst open. "What?!" Star Swirl exclaimed, caught by surprise by the sudden calamity. He whipped around and looked behind him and his eyes widened in horror.
Standing in the doorway was Princess Luna, who seemed to be struggling to control her own body. Violent wisps of the inky black power were uncontrollably manifesting themselves around her body. "S-sir!" she groaned, calling out to her mentor. "P-please help...help me!" Her teeth were clenched as she tried to push back the overwhelming entity that was taking control of her mind, her eyes ablaze with panic.
"Oh my goodness, Luna!" Star Swirl said, quickly assessing the situation. He charged his horn and fired a bolt of magical energy towards the princess. However the black energy that was enveloping the princess counteracted the magic and deflected it. "No!" he exclaimed in futility.
The swirling dark magic had gained enough form to engulf Princess Luna in a sphere of blackness. The swiftly-spinning energy managed to whip up a strong wind current in the room and began throwing objects around with no regard, scattering Star Swirl the Bearded's equipment and papers everywhere. Star Swirl held up his forehoof to protect his face from the gusts being created by the swirling energy.
The magic began to settle and receded around Luna's hooves. However, as it revealed the visage of the princess, her appearance had undergone a drastic change. Luna's graceful alicorn wings had given way to aggressive wings that came to a point at their tips. Her coat was no longer a dark blue but pitch black while the crest on her chest had transformed into a plate of armor bearing the icon of the crescent moon. The small metal guards she wore around her hooves had grown in size and now reached her shins while her head was encased in a helm that covered the back of her neck, the horn on her head having become much longer. The color of her eyes had changed from a soft white to a light blue while her pupils were now thin slits.
The alicorn laughed with a devilish glee, which echoed down the halls of Canterlot Castle. It was the deranged and chilling laughter of a tyrant.
"Mmhmm hmmhmm...ha ha ha...HA HA HA HA...AH HA HA HA!!!" She glanced at Star Swirl and grinned maliciously.
"Weak old fool..." she chided, unimpressed by Star Swirl's magical ability. The alicorn covered herself in a shroud of magical energy and vanished into nothingness, leaving Star Swirl alone in his now-destroyed laboratory.
"This is terrible..." Star Swirl said to himself in despair, shaken and disturbed by what he had witnessed. "How...?"