"Nightmare Night, what a fright, gimme something sweet to bite!"
She loved being a bat pony that year. The very same year Princess Luna had her super cool bat pony guards, it made for the perfect Halloween costume. She figured everypony would love the cool armor she made for the front of the body. It didn't even occur to her that it was the back part of her body they might be interested in.
When the big, blue stallion smiled down at her craftily, and said "I just ran out of candy, but I have more in the kitchen if you'd like to come in and get it," she was no dummy. She figured something was up, and her parents told her to never go into the house with a strange stallion if he asks you to. One of her friends said that this stallion was the best though, but was kind of confusing about it. She said that she shouldn't go in the house with him, but sort of made it sound like it'd be really good if she did.
So giddy with her own rebellion, she decided to find out just what her friend wouldn't tell her about, and what her parents told her not to do. Plus if he had some kind of super special candy, she couldn't wait to try it! "I can really get candy?" she asked warily.
"You sure can," he said, making way for her to come inside the brightly lit house.
She made her way to the kitchen, where there actually was a bowl full of candy sitting there. It didn't look like anything special though, so she was nosing through it trying to find if there was anything she didn't already have.
She reared up in surprise then because the stallion climbed right on top of her! Her forehooves clopped down on the kitchen counter as something big and slimy pushed against her, between her spread hind legs. Frightened, she lifted up off the table, but he held her down and pushed and it started sliding and stretching. Her fillyhood ached with a strange hunger, as it got stretched wide around this thing. Her eyes lost focus, feeling the thing sliding deeper and deeper into her.
He didn't say anything, just shifted against her to pull it out, then push it in again, then pull it out, then push it in. He started doing it over and over, and everything that he was sliding against in there was tingling. It was like scratching an itch she never knew she had. Her heavy breaths turned into vocal moans, as the sound of his hips slapping against her bottom were matched by that incredible sliding sensation.
She arched back, pushing against his hips, trying to get his thing even deeper. She found herself staring distractedly forward at the bowl of candy, and it was so strange. She forgot she was getting candy at all. She didn't even want the candy. All she wanted was him to push into her again and again, with the tingling and the sliding, and her bottom just opening for him, as she pushed back against his penetration.
The tingling itch scratching satisfying feeling got bigger and bigger, and soon she was just gasping in strange wonder, only thinking about her fillyhood that she couldn't stop squeezing around his thing. She squirmed and pulsed in her vagina that she only barely knew about, every rhythmic clench filling her mind with stars. She loved having a... thing sliding inside her!
Then it got even better! She was coming down from that... thing, her whole body tingling as she indulged in her new urge to mate, wondering how long he was gonna do this in her, when he shoved deep and stopped. She cried out as he shoved deep, because something just burst from his penis, spurting even deeper into her, something hot, smooth, and slimy. Then he did it again and again, spurting his seed into her inside place, splattering it all over her uterine walls.
She panted gladly with her tongue out, as his strange stuff did things to her in there. She loved every time it squirted, and filled her with this hot... stuff that warmed her belly with a strange satisfaction. Squirt, squirt, squirt, she took it all. And the pulses started to lessen then, until the thing was quiescent inside her, and the strange fluid was just pooling warm in her belly.
"What..." she gasped, "What was that?"
"I impregnated you," he said, hugging her hindquarters warmly. "Do you know where babies come from?"
"...mommies?" she ventured, unsure of this whole situation. "What is in me?" she asked passionately.
"It's my penis," he said affectionately.
"Your penis?!" she asked disbelievingly, and she'd seen penises before, but... what?
"I can feel you with it," he said affectionately, "You feel so good in there. My penis gets big, and hard, and I wanna put it into fillies and rape them like this.
"Rape them?" she asked, looking over her shoulder at him, her forehooves still perched on the counter.
"That's when a stallion puts his penis into you without asking," he said unrepentantly, looking back at her in amusement.
"But I really liked that," she said in astonishment, "Why would you even have to ask?"
"Did you feel my semen going into you?" he asked curiously.
"Yes, and that was the best part!" she declared, "You can do this I don't mind if you don't ask it's... it's awesome!"
"H-here, sit down on my lap," he said, pulling her back. Without sliding out of her, he got her to sit on his lap while he lay down on the kitchen floor, and told her, "There, can you see me going... into you?"
She stared with fascination at the stallion's dark blue hips pressed to hers. She felt him sliding before she saw it, and out of her hips, his gleaming, dark shaft slid. Then she felt it pushing back, and it slid inside her again. Very slow thrusts, just sliding out to show her.
"Alright now... all the way out," he said, pulling her hips toward his chest. She was too busy gawking at his penis sliding out and out of her, more and more, until this giant penis just sort of slid out of her.
"H-how?" she squeaked, as he flexed his shaft before her groin, "Did that fit in there?"
"You're made for it to fit in there," he said, "My sperm is deep inside you right now, and if I'm lucky, it's gonna swim around in there until it finds your egg sometime tomorrow. Then you start turning into a mommy."
"I... I do?" she asked, a little apprehensively.
"That's why I'm supposed to ask," he said, "But I think you already wanna be a mommy. Your belly's gonna get big and round," he stroked a spot right by her teats, "..,here. You're gonna have a foal growing big and strong inside you. And one day, when they're ready to be born... you're gonna get the urge to start pushing."
She listened in utter fascination, as he said, "A little at first, but then more and more, until after about a day it's the only thing you can think about. Just squeezing your belly and pushing out your foal. You know where my penis went, right?"
"Yeah?" she said thoughtfully.
"Imagine pushing, squeezing your belly as hard as you can, so a foal just squeezes outta there," he said temptingly, "That's what's gonna happen to you now. You're just gonna be sitting there, watching a foal squeeze out from between your legs. It might hurt, but you're gonna want it so bad, you'll do anything to get that foal out. That's what giving birth is."
"A-and I... stretch big when that happens?" she asked, lost in the fantasy herself, imagining her groin just bursting forth while even her legs stretched apart.
"Yeah, and your teats start producing milk," he said, touching each of them, "Your foal will stand up then, and you can stand there while they suckle on you. Just like you suckled at your mommy, and she suckled at her mommy's teat. So I just made you a mommy, just like... your mom."
"Wow..." she said dazedly, "I never even thought... so my mommy had a... penis inside her?"
"That's right," he said, "And he squirted seed inside her just like I squirted seed inside you. You started growing in there, because your daddy's sperm turned your mommy's egg into... well, you. Once you were ready to be born, your mommy got to see you squeeze out from between her legs. And now that's gonna happen to you too."
"A...a foal's gonna just... grow in there?" she asked.
"It's gonna be a real pony," he asserted, "Maybe even a filly. And one day your filly's gonna go out on nightmare night, and come back with seed inside her."
"And then she'll..." she said softly.
"I'm sure you can help her with it," he attested, "Just pay attention while it happens to you now, and tell her what it was like. In fact, ask your mommy about when she had you inside her. She can tell you about how you're gonna chance, to be better at being a mommy."
He floated her out of the house, cum dripping from her vagina. She just hung there in his magic, dazed, not even noticing all the candy he was giving her, just kind of... thinking about being a mommy. "Enjoy the rest of your night," he said shrewdly, "I sure will."
"H-how so?" she asked curiously.
"I'll be enjoying just thinking about how my sperm are inside you right now," he explained, "Searching around for your egg to make you pregnant."
...
Later, as she grunted, and pushed, and birthed, and she needed to nurse her foal from her aching teats, she moaned, "Best nightmare night ever."