Since ancient Equestria, mothers told tales of the evil Mare in the Moon; Nightmare Moon coming to haunt their childrens' dreams if they were ever disobedient over bedtimes. Most fillies and colts believed the tale, while the more daring ones attempted to tempt fate by staying up for as long as their young, tired bodies allowed them to.
Things were no different at Canterlot Castle, where two young princesses were told the same old tale by one of their nannies, if not by Empress Celestia herself, however reluctantly. For a first-time mother with little to none experience, the trick was helpful to get her children to bed, as much as it stings her lonely heart to do so. Princesses Sunset and Twilight would scramble to bed almost immediately at the mere mention of the name of the feared mare.
It worked, until the girls stopped believing that going to bed on time would grant them protection.
For nothing could protect them from the guardian of dreams herself.
While her embodiment was locked away, trapped on the moon - her spirit roams free, waiting for the right moment to make herself known. Princess Sunset Shimmer - heir to the sun and first-born daughter of Empress Celestia, dreamt of darkness during one fateful night.
On the longest day of the thousandth year, the stars will aid in her escape, and she will bring about nighttime eternal.
The prophecy echoed in her dreams. It continued to do so for several days - until she saw her; a dark coated mare with an ethereal mane so magical it flowed by itself, floating midair in a place scarce of wind. She emerged from the darkness, with a look so gentle in her eyes that the filly would have given her a warm greeting if it weren't for the spine-chilling surroundings. The strange mare loomed over her, so tall that she could almost surpass her own mother in height.
"Shh young one. I mean no harm." The mare cooed at the sight of the little princess's shaking figure. "For I could not cause harm in the dream realm."
This mare is an alicorn. Sunset had never met an alicorn other than Empress Celestia and Princess Cadance, and from that experience, they are plenty powerful. If she wanted to, this mare could burn her to ashes. Should she be afraid? Is this mare dangerous?
"I sense you have questions, young one." The mare spoke again, a slight edge to her voice as she silently struggled to maintain her form.
Her curiosity defeating her perception for caution, Sunset nodded. "..W-who-.." She gulped, taking note of the dark mare's muzzle lowering itself to watch her height.
"Who am I, young one?" She questioned delicately. The little filly nodded again, trying her best to not appear too eager. A little information is always a golden opportunity in any circumstance.
"I am but a myth." She cooed again, folding and unfolding her wings as if proving to Sunset that she is real. "You may know me as Nightmare Moon, as I have been rumored to haunt dreams, and some have claimed for my sihouette to be visible on the surface of my prison; the moon."
"A-are you..? A rumor?"
A smile. For a split second, Sunset could see malice haunting the ancient mare's features before it immediately shifted to a far kinder look - a look one would see on an overbearing grandmother. "Tell me, young one. Do you believe I am such? Could your dainty, youthful mind possibly conjure such a magnificent being such as I?"
"I.. guess not. Usually I just dream of being on a walk with my mom, spending time with my sister or learning some ultra cool magic stuff... Oh, sometimes I dream about becoming the next Emp-" At the stranger's look of detest, Sunset ended her rambling and lowered her gaze, ashamed and fearful.
"Do you know why I chose to visit you tonight, young one?"
"Are you.. r-real? I thought you're just a dream."
"That I am not." The mare exhaled patiently, recognizing the amount of patience conversing with the filly is going to take.
"O-oh..." The little princess backed a few steps as she realized how close the mare had gotten to her. Unfortunately, it only took a small stretch of the neck for the older alicorn's muzzle to remain only a few inches away from her own. There is no escape. "Why are you here?" Sunset braved herself enough to ask.
"Why am I here? Better question is, my child; why are you here?"
"Huh?"
"I am Nightmare Moon, the figment of power I was denied. I was borne from desire; a desire to rule, to gain power, to be loved - the presence of whom deserving to be relished by many throughout the generations." Her eyes glowed white, so bright that it illuminated her dark face. She forced her facade into Sunset's vision, her pupis narrowing into slits as she did so - the light so hypnotizing that the filly was unable to look away. "I would not have been able to enter your dreams tonight, Sunset Shimmer - if you do not have that in your heart as well."
"I... no!" The filly screamed, pulling away from the contact. "My momma taught me to be good! To be a good princess, a good sister!"
"But your sister outshines you in so many ways, does she not?" Nightmare Moon pushed on, her voice now back to the soft coo she held upon her initial appearance. "You could be so much better, you could be loved so much more. You could be admired-"
"No! I'm happy where I am." Sunset contradicted. "I have so many things to be grateful for. I can't ask for more!"
"That is what your precious mommy told you, is it not?" However impatiently, the gentle, reassuring coo is not lost in her voice. Nightmare Moon attempted a strained smile despite the annoyance she felt. "My dear Sunset. There is so much more you could get out of life. So much more that you deserve."
"I... I..."
"Wouldn't you just love to sparkle much, much more than your sister? Wouldn't you love to just loathe her?"
"I love Twi-why. She's my sister! I could never hate her!"
"Not even for your fair share of love from a mother?" The mare's pupils had returned to its original shape, though the discomfort it created earlier remained.
"Momma loves us equally. She said so." Tears had started to form in the filly's eyes. Nightmare Moon smiled at the sight of the princess's misery.
"My dear," Nightmare Moon pressed, "A mother lies."
That is when Sunset stopped listening, stopped caring, stopped bothering to even try and understand the nightmare she is experiencing. Is her heart really that selfish? She is far too young to have such thoughts. Her mother raised her to be good. Her mother told her she is good. Could it all just be a false truth, all for her to be misled to a path her mother had so ambitiously carved for her, further away from her destiny?
"Alas child, you are about to return to the waking world. I shall not be able to remain here any longer." She heard Nightmare Moon's voice echo into the void. Her sight had become so blurred from the tears, all she could see is endless darkness.
"Please stop leaving sweets in my wake. It is a mockery to be offered such pleasant offerings, but not be able to satisfy my taste-buds with such luxury."
Then there is silence. All Sunset Shimmer could hear is her own thoughts; thoughts so intruding it plagued her mind and body; causing her to shiver non-stop, not allowing the river of tears to end. She didn't realize when her consciousness had returned to the mortal world, or if it even did. She didn't feel her sister shaking her quivering body, didn't react when she ran out of their bedroom in a panic. She isn't aware of anything, until a soft warm glow brought her back to full consciousness.
Her mother's face illuminated her view, and her cries of horror immediately dissipated into cries of relief. She clung to the Empress like a lifeboat, refusing to let go. This is reality, and she didn't want to lose it.
"M-mom- Momma... Th-there was t-this mare...-"
"Shh, my love. It was just a nightmare."
A nightmare. Nothing more.