The First Nightmare Night
Long ago, in a certain village, there was a poor pegasus. She was young and very kind, but homeless.
One fateful day, the moon blotted out the sun, bathing the countryside in endless night. The ponies of the village soon heard terrible news: Luna, Princess of the Night, had given her heart to bitterness and had become a wicked mare of darkness: Nightmare Moon.
Nightmare Moon was bent on bringing all of Equestria under her iron hoof, even if it meant ruining the whole world. She flew all over Equestria, bringing terror to those who had loved her sister so much more than they had loved her.
The mare had nothing but the clothes on her back, but she loved each pony in her little village, so she decided to plead with Nightmare Moon for their sake. She took up her cloak and went to the villagers to seek tribute to appease Nightmare Moon. She knocked on each door, asking the same thing.
“Please, let us give tribute to Nightmare Moon, that her wrath may pass us by.”
Door to door she went, but everyone turned her away. Either nobody believed her, thinking she was a beggar, or nobody was brave enough to face Nightmare Moon to offer tribute.
The mare asked every last pony in the village, but she did not find a single thing to offer to Nightmare Moon. She began to cry, knowing that her village would soon be destroyed if she didn’t do something.
Then she had an idea.
“If nopony will offer anything to Nightmare Moon…then maybe…I can offer her something myself,” she thought.
She went into the woods toward Canterlot, and there in a clearing, she waited for Nightmare Moon to come.
Soon, she saw the dark princess flying among the stars, and she took off and called out:
“Mighty princess, please accept our offering and spare our village!”
Hearing the mare’s voice, Nightmare Moon turned curiously towards the sound, and she descended to address the pony who dared to speak to her.
Nightmare Moon sized up the poor mare and laughed. “What have you to offer me, mortal, that I should spare your people?”
“The only thing I have,” the mare responded. “My life.”
Nightmare Moon remained silent, her face mildly amused.
“…My whole life. Please spare this village, and I promise to serve you until the end of my days.”
Nightmare Moon narrowed her eyes. “You would give away your life for these treacherous ponies? They have given you nothing—as much as they gave me!”
“I will…your Majesty. I love them. Please…this is all I have to offer.”
Nightmare Moon paused to consider.
“Your offer amuses me, mortal, but unfortunately, my fury is not so easily appeased!”
The mare’s face fell, but Nightmare Moon continued.
“But perhaps…I have a use for you.” Nightmare Moon thought for a moment. “The price for my mercy shall be this, then: not only yourself, but your firstborn, and all the firstborn of all your posterity until the end of time!”
Boldly, the mare responded without a thought. “Be it unto me as you say; I accept these terms!” she pleaded.
Nightmare Moon touched her horn to the young mare’s forehead, and a shadow engulfed her.
“Then for all time…you shall serve…the Princess of the Night!”
The mare emerged from the shadows, no longer a pegasus. Her body had fused with that of a bat--her feathery wings became leathery and black.
Her frightening appearance saddened her, but she smiled for her people, and she bowed before her new master.
“Thank you…my Queen.”
That night, Nightmare Moon did, indeed, pass by the mare’s village. After hearing of what the poor mare had done, the ponies of that village were so grateful for her sacrifice that they held a festival for her.
True to her word, the mare served Nightmare Moon in every waking moment. Nightmare Moon was soon defeated by Princess Celestia, and the mare returned to her village, where she eventually married and had foals. As Nightmare Moon promised, her firstborn was what we now call a bat-pony, and their posterity continues to this day. The cursed mare and her family never forgot their covenant with Nightmare Moon. Generation after generation, they waited for the day when their Princess would return.
Twilight Sparkle closed the book.
“The firstborn descendants of that mare serve Princess Luna to this day, and every year, children go door to door as she did, asking everypony to give tribute to Nightmare Moon. That’s how the villagers decided to remember the mare’s sacrifice. They symbolically gave what they initially refused to. Some of the details of the observance have changed over the years, but that’s how Nightmare Night really came to be.”