Author's Note

This is intended as an idea dump of sorts for my own story concepts. Please do not solicit your own ideas.

Prompt: Nightmare Moon has just unbirthed Twilight Sparkle, now looking hugely gravid. She now intends to unbirth the rest of the Mane Six. As she does this, she slowly absorbs the power of the Elements of Harmony (the relics), slowly growing larger and larger. The growth is slow to happen, but Nightmare Moon’s lust for power gets the better of her, and she unbirths the Mane Six faster than she can absorb the power. It overcomes her and reverts her to Princess Luna… but she’s still huge (in both stature and belly). Later, Celestia comes and finds Luna, who reveals that Twilight and the others have been changed into alicorns, and look similar to Luna.

Contains: Feral, Unbirthing, Pregnancy, Growth, Macro, Alicornication.

Can't directly link the pic for this one as it's NSFW. Go to derpibooru.org, put in a slash at the end, and type in 874366.

Well, That's One Way to Do It

“Ahahahahaha!” Nightmare Moon squeezed her groin muscles one final time, relishing the feeling of her cervix closing around Twilight Sparkle’s legs. She grinned a wolfish smile as her body glowed with the newfound power, the Element of Magic connecting to her, it’s energy seeping into her.

“Yes… YES!” Nightmare Moon’s body crackled with newfound power. Her belly looked heavy with foal, well past due with a healthy set of triplets… or one adult mare. Said mare had been comatose the moment she’d been fool enough to be locked alone in a room with her.

“Mmmm…” Nightmare Moon patted her bulging womb, heavyset between her legs and nearly grazing the ground. “So… much… power!”

“Twilight!”

Nightmare Moon flicked her ears. Ah, yes… she’d forgotten about those other five, the other prospective Elements. They were making their way up the tower, and the power of the relics had already been transferred to them, it seemed. She could sense it coiling around their souls, not yet fully latched.

“Perfect.”

Nightmare Moon unlatched the ancient, oaken door, but still gave it the appearance that it was shut fast. Sure enough, a few seconds later…

BAM!

“Whoa!” The five mares all tumbled into the room in a mass of manes and tails, the door swinging wide open for them.

Nightmare Moon rolled her eyes. It really couldn’t be this easy.

ZAP!

An instant later, all five mares were comatose, just like Twilight Sparkle had been.

“I’m not taking chances with you five,” Nightmare Moon growled. With some effort, she made her way over to the pony pile, her gait slow and waddling. “The last time I underestimated the Elements of Harmony, I spent a thousand years on the moon.”

She examined the five mares, her nostrils flaring. She could smell the newfound power on them, tantalizing.

“Never again will it be used against me.” Nightmare Moon turned her back to the remaining Elements, her tail lifted high. Beneath, her navy marehood lay dripping, its petals winking for what was to come. “I will absorb it from you all before it fully latches onto your spirits! It will be mine! MINE!”

Nightmare Moon lifted the topmost of the ponies in the pile, a yellow pegasus with a pink mane. She was slender and willowy, with a wide set of hips. Nightmare Moon placed Fluttershy at the entrance to her nethers, then greedily, began to push her inside.

It felt just like it had with Twilight Sparkle. Nightmare Moon moaned as she felt her labia widening, engulfing the legs of the mare. Her inner muscles sucked Fluttershy in, bit by bit, Nightmare Moon shivering as already, the power began to be drawn into her.

“Gooooood…” Nightmare Moon’s eyes sparked, glinting with the siphoned energy. She barely even needed to guide the process, her vaginal muscles did most of the work themselves. The unaware Fluttershy was pulled into Nightmare Moon’s cunny, her legs disappearing… then her hips… then her stomach…

Nightmare Moon felt the weight being drawn into her center, her dark, powerful womb. There, the magic truly did its work, absorbing the power of the Element and adding it to Nightmare Moon’s might. It was like an adrenaline rush times fifty, her heart pounding with a bubble of hot air rising in her chest, addicting and yearning, commanding her not to stop.

The power coursed through Nightmare Moon, empowering her. Her body glowed with eerie light, and slowly, steadily, she began to grow. Her limbs stretched and lengthened, her bones and muscles becoming bigger, stronger, denser. Her frame elongated and lengthened, her organs groaning as they swelled. Six feet tall became six and a half, and six and a half became seven. She gained another half foot atop that before it stopped, and all the while, her belly was burgeoning even more, filling up with fluids, magic, and tissue, all to support her ‘prey’ while she took their magic.

With a loud, lewd slurp, Fluttershy’s head disappeared inside Nightmare Moon’s cunt. A few seconds later, she was fully inside Nightmare’s womb, connected as a mother was to their child. Nightmare Moon cackled madly. She was still absorbing power from Twilight Sparkle, and this one had a good deal, too! She was going to be UNSTOPPABLE!

“Two down,” Nightmare Moon said. Her forked tongue snaked out to lick her lips. “You four are next…”

The next was a pink earth pony with a fair bit of cush to her. Healthy fat, Nightmare Moon realized. There was a good bit of muscle underneath it. She wasted no time in bringing this one into her womb, as well, crying out in ecstasy the very moment their bodies made contact.

“YES! MORE!” Nightmare Moon squeezed her muscles harder, drawing in Pinkie as fast as she could. Her ebony body groaned as it gorged itself on the newfound power, the growth beginning anew, but faster… stronger! She could feel her hooves pushing away the ground, her vantage point slowly rising. The ceiling drew closer and closer, Nightmare Moon growing past eight feet… then nine… then almost ten! The ancient stones cracked beneath the pressure of her growing magic, the air becoming thick with her might!

Nightmare Moon screamed as an orgasm hit her. The incessant, hungering clenched exploded into fireworks, her mind clouding over. Her silky walls spasmed all the faster, drawing Pinkie in all the way and sealing her inside Nightmare Moon’s womb. The energy of the Elements was swirling about all three of them, ambient and collecting, slowly being absorbed into Nightmare Moon’s walls.

It was on autopilot that Nightmare Moon reached for the fourth mare, a white unicorn with an indigo mane. She was shoved unceremoniously into Nightmare Moon’s hungry marehood, which enveloped her eagerly. There was another spark as Rarity and Nightmare Moon touched, and the room rumbled as Nightmare Moon grew faster, and faster! She grew to twelve feet in a mighty surge, then a second surge right after pushed her up to fourteen! Her head smashed the remains of a chandelier, reducing it to nothing but rubble. Her horn grazed the remains of the ceiling, but it soon was doing far more than that as a final surge or growth pushed Nightmare Moon up past fifteen feet!

“Power... “ Nightmare Moon’s voice was laced with a faint echo, her eyes now shining bright. “POWER!”

Her belly sank even lower as it accepted its fourth progeny. Now a giantess and pregnant with four fully-grown mares, Nightmare Moon let out another crow of triumph.

“So much energy inside them!” Nightmare Moon rubbed her enormous paunch, gasping from the resulting jolt. “It’s increasing for every one of them I take!”

But that didn’t stop her--it excited her. Before she could stop herself, she’d taken the last two ponies, an earth pony and a pegasus together, placing them belly to belly against one another. She then pressed them both to her enormous, sopping flower…

“AHHHHH!” Nightmare Moon saw white. The power of the remaining two, it amplified the others exponentially! She couldn’t stop it if she tried, though, her body had a mind of its own by this point. Her tunnel sucked in Applejack and Rainbow Dash with a wet, organic SCHLICK, her pussy stuffed full with the combined size of two powerful, muscular mares. Now Nightmare Moon was the one rumbling as the energy was added to what she’d already absorbed, her body shaking in preparation.

“Oh…” Nightmare Moon panted for breath. “OH! OH, YES! YES!”

Her head broke free of the ceiling in a pulse of grumbling growth. Her legs smashed the back walls of the tower, leaving the rest to collapse all around her. She rose into the air of her own accord as she grew past twenty feet, then twenty-five, and finally thirty!

“MINE!” Nightmare Moon cried out to the heavens. Applejack and Rainbow Dash slurped inside her cunny, then fully into her womb. “ALL MINE! THE POWER OF THE ELEMENTS IS—”

As soon as the six were fully inside Nightmare Moon together, their comatose forms glowed with prismatic light. The harmonic energy had been gathering faster than Nightmare Moon could absorb it, and now, it was coalescing into a single, all-encompassing force.

“What?” Nightmare Moon felt the power shifting, now rebelling against her. “Wait, STOP! NO! NOOOOOOOOO—”

From within, a cocoon of rainbow energy enveloped Nightmare Moon. There was a deafening sound like thunder, followed by a blinding FLASH.

Princess Celestia flew as fast as she could to the old castle ruins. The spell that’d banished her to the sun had been lifted, but she sensed that something was… off.

Upon drawing close to the castle, she saw exactly what ‘off’ meant.

“Luna?!”

“Erm…” Luna waved with a cart-sized hoof, careful to remain still as her sister neared. “Hello, Celestia! ‘Tis good to see you once more!”

Celestia did a double-take. Luna was the size of a three-story house! What the hay?!

Luna coughed politely, her cheeks a faint shade of pink. ““I, ah… can imagine what you must be wondering. I don’t quite recall, myself. Although, based on the appearance of your pupil and her friends, I think I can venture a guess.”

Celestia gasped. “Twilight Sparkle! Is she—”

*cough*

Celestia hesitated. Either she was hallucinating, or Luna’s mane was coming down with a cold. There was a few seconds of silence before Luna finally sighed.

“You may as well show her.”

There was a reluctant groan. Finally, a pale blue alicorn mare emerged from behind Luna’s neck, with a familiar streak of pink in her mane.

“H-Hi, Princess Celestia…”

Celestia’s eyes nearly bulged out of her head. “Twilight?!”

“And I’m afraid it’s not just her.” Luna gestured to the ruined courtyard.

There, emerging from various places, five more pale blue alicorns showed themselves, waving sheepishly.

“Hi, Auntie Celestia!” Pinkie shouted. “I heard that you like cake!”

Luna had to catch Celestia as she fainted.