Nightmare Moon
A thousand years of banishment served merely as herald to Princess Luna's return to power. For a millennium she'd dreamed of a rematch with her sister, of putting that meddling mare in her place and claiming the hearts of her subjects once and for all. What she got instead was Princess Celestia's pawns, foolish fillies whose plan consisted of little more than a scavenger hunt and wishful thinking.
It was almost too easy.
Now, she stood upon the broken throne of her dark castle tower. Moss and vines wrapped each pillar and stone. The moonlight shone through every crack and broken pane, casting aglow her midnight fur and starlit mane. Once her prison, now the light fueled her power and bid the ghoulish palace to awaken. She stood in the height of her glory, the Elements of Harmony and Celestia's pawn broken at her feet.
“The night will last forever!”
Each moment in the growing night filled her with power and pride. She laughed to the heavens, but still caught the sound of five more ponies ascending to her chambers.
Twilight Sparkle's new-found 'friends' managed to foil each of her obstacles. Each of the five ponies embodied their elements. Applejack, the earth pony who had entrusted her friend's fate to another. Fluttershy, the quiet master of beasts. Pinkie Pie, who dismissed the faces of danger. Rarity, who pacified the serpent with her flattery. And Rainbow Dash, who knew her own ambitions and refused to be swayed.
Her sister had brought them all together so that they could turn the Elements of Harmony against her again--so that her protege could finish what she had started.
The sixth Element manifested before Twilight Sparkle. The unicorn pushed herself to her feet and stood defiant. “You see, Nightmare Moon... when those Elements are ignited by the spark that resides in the heart of us all, it creates the sixth Element: the Element of Magic!”
Another light engulfed the ponies as the Elements of Harmony began their work. She had seen this only once before, when she and her sister had been accepted element bearers. The broken shards reformed and the magic became whole once more. The six ponies stood before her and from the will of harmony came waves of prismatic light.
The rainbow spiraled upwards and then crashed down on Nightmare Moon in a deluge. She screamed out in pain and fear as the magic twisted about her, the colors forming a blinding torrent that pushed deeper and deeper into the core of her being. She would not go back. She would not let her sister win again. Yet she could not fight back.
She thought it was over. But the Elements of Harmony did not seal her away as they had before. Instead, she found herself in the darkness of her mind, each aspect of herself split and laid out before her. A timeless space in which the will of Harmony was granting her a choice.
Down one path lay peace, forgiveness, and transformation. The love of her sister and all of her friends promised to her. A future of prosperity and happiness awaited her, should she seize it. A vision of the same future that'd been promised before her fall. Before the nightmare began.
There was another path, though: a path that led to night everlasting, pain and suffering, revenge and madness.
Love is all you've ever wanted, she told herself. All you've truly wanted.
And then another voice, also her own. You've been fooled before. Celestia's kindness can never mend the past.
For all she would become, the thought of even a moment of surrender, of being powerless beneath Celestia, twisted her guts like a bellyful of fouled grass. Her heart ached to become the mare she once was—no, the mare she'd always desired to be.
Help me, she begged herself. Help us. It's not too late.
Who would she forgive? The guards who had failed her, the friends who had forgotten her, the loved ones who'd fallen from the mortal coil? Her sister, perhaps? Nightmare Moon was strong and stubborn enough to overcome herself, in most cases.
But twisted in the depths of her psyche there was no other pony she hated more than herself--for her weakness, for allowing herself to be hurt and manipulated.
The light was patient. The light was infinite. It would hold her still in time until she'd made her decision. And all she could do would be to accept their offer with grace, and return to Equestria.
No, her other self thought.
“No!”
Two destinies unwound from a single thread. A fork split in the crossroads of time, and as if succumbing to some itch, some primal drive, she railed against Harmony. The time for love and forgiveness was long past, and she chose vengeance. She called upon all the power of the moon and all of the magic within her, and unleashed it upon Harmony.
Harmony, gentle Harmony, with its olive branch extended, with its sureness of love and forgiveness, for just that moment became the most fragile thing in the universe. And she shattered it.
The explosion of magic rocked the castle. The Elements of Harmony, so soon after being reformed, crumbled about their bearer's necks. Shock waves of magic threw them to the ground and the light dissipated, leaving only that of the moon above. Nightmare Moon pushed herself upright and flared her wings.
“I admire your spirit, Twilight Sparkle,” she said. “But there is nothing in the world that can stop me now. You have failed, and so my sister has failed." A maddened smile appeared on the dark mare's face. "Do not fret, though. There is a place in my Equestria for everypony.”
Tears fell from Twilight's eyes, vanishing into the cracks in the stone floor. She mouthed Celestia's name, and then joined her friends in unconsciousness.
So began what all of Equestria would remember as the Longest Night. Nightmare Moon broke the will of Harmony in order to reclaim her throne.
And deep in the gardens of Castle Canterlot, upon a statue most forgotten and ancient, the first crack formed.