Twilight's breath hitched. She had seen many things in Equestria before, but the mirror pool cave was something completely new to her. Most caves were dark and wet places where light was scarce. This cave however, seemed different. Instead of loose moss and mud, the ground was blanketed by soft grass that felt more akin to carpet than foliage. Bioluminescent plants littered the cave outside of the patch of light shining in, and the entire space seemed well lit despite there being so few external light sources.
She stepped toward the pond and looked it over carefully. The water acted just as the legends in the book told. It did little but shine her own reflection back while seeming to hide much more from her inquisitive eyes just below the surface. She could see no algae or plant life making their homes in the pond leaving her to wonder if it was even corporeal or just a magic barrier.
I know I'm here to seal it up, but that doesn't mean I shouldn't study it first.
Twilight gently lowered her hoof to the water and tapped it's surface. It felt real to the touch. In fact, when she pulled her hoof out, a bit of the water clung to her, acting more like syrup than water.
"Thats odd. Pinkie said she didn't get wet at all."
Twilight tapped the surface again. This time the water started crawling up her leg. She frantically shook the water off her hoof. Frightened, but still intrigued by the behavior, the unicorn sat down in front of the pond and stared at the water. The droplets hit the surface, but didn't merge with the rest of the water.
Slowly, the water rose up out of the pond in the shape of a pony and crawled out of the pond. Twilight was speechless. Perhaps the water was not just simple magic or water, but instead a sentient creature!
The pony, still the same color as the water stared at her blankly.
Twilight decided the best thing to do would be to try and communicate.
"Ummm... Hello there. I am Twilight Sparkle, can you understand me?"
The water pony didn't react. Instead, it stared at Twilight, considering Celestia only knows what.
"Can I help you?" Twilight offered.
Without warning, the figure lunged at Twilight knocking her on her back. Twilight struggled but couldn't stand up. The figure's hooves melted around her legs keeping her pinned.
"Ungh! What are you doing?!"
The creature looked Twilight up and down studying her intently. The unicorn stared as a protrusion formed between it's legs growing thicker and longer.
"Oh no you don't!" Twilight aimed her horn at the figure, but before she could react, another piece of the pony detached and landed on her horn fizzling the spell.
"My horn!" Twilight cried out. At first she began to panic, her breathing and heart rate increasing dramatically, but a soothing, cooling sensation spread from her horn. A calming sensation overtook her easing the stress. The figure poised over her lowered itself closer and touched Twilight's sex with its newly formed cock.
"No, no... I'm saving myself!" Twilight pleaded. Part of her wanted the creature to continue, the other half screamed at her to escape. Her entire mind flooded with pleasure and pain though as the creature's substantial cock penetrated her.
"N, no!"
Twilight screamed. She felt the smooth member hit her wall, that part that reminded her she was untainted by the feel of a stallion's pride. The creature pushed through it forcefully. Twilight cried out as it slid past. Drawing in gasping breaths, the unicorn looked down at the creature's cock and saw her fluids on the mirror like appendage as it slid in and out. She only got a moments reprieve though before the creature thrusted again, this time easier and less painful.
"N, no... Why?"
The creature seemed unapologetic as it started pounding itself in and out of her now dripping sex. Twilight felt a sea of pleasure rising in her mind as the creature pounded harder.
"Ungh, yes! More!" Twilight pleaded. She was now a slave to the pleasure as the creature gave titanic thrusts to her now sore cunt.
Twilight's mind flooded with pleasure as the creature hilted itself fully inside her. She came, bucking against her intruder's cock as a cool feeling spread through her marehood. She felt pressure and fullness each increase in her desperate sex as she realized the creature was shrinking. Each thrust from the creature poured quart after quart of the liquid inside of her narrow canal.
"Ohhhh yes! More!" She screamed.
Twilight shuddered as her belly started growing in front of her eyes and she soon saw why. The creature wasn't filling her with its semen, it was filing her up with itself! Twilight gasped as each burst sent more and more of the figure into her marehood pumping right into her womb. Her hooves, no longer being held by the creature, flew to her expanding belly as she sought more pleasure. The tiny bit left of the figure formed into a blob and squirted into her canal leaving her gasping and rubbing her belly which looked like it held a full grown pony. She laid on the ground panting as she digested what had just happened.
"Oooooooh... I'll never be able to move like this." She groaned out. Seemingly in response, she felt her stomach churn. What sounded like sloshing water intensified as she felt her belly being pulled one way and then the next like a jiggling water balloon. She felt something tickle her insides momentarily before it halted.
"Hoh boy! Ungh!" Twilight grunted in pleasure. She felt her belly surge forward rising a foot in height and expanding about as much in circumference.
Toxic pleasure poisoned her mind as she begged for it to happen again. She was obliged by another growth spurt knocking her on her side. Her massive belly now looking like she was ready to give birth to five foals slammed on the soft grass with an audible slosh and wobble sending her rolling until she sat atop her massive belly stretched out beneath her. Every touch, every shake and jiggle felt like direct contact with her erogenous zones. The sensitivity of her skin seemed impossibly high as her belly surged forward again, taking up another two feet of space.
Twilight began to panic when she realized her hooves were useless. They flailed and swung back and forth alongside her belly completely and utterly unable to move her.
A new sensation took hold halting her escape attempts. She felt rising pressure building in her belly as the massive mound she was stranded on top of started growing again. She couldn't begin to guess how big she was now. She just knew that she was bigger than any pony she had seen before sitting several feet in the air.
With a sudden and jarring halt, her belly stopped growing leaving her to wobble slightly. Her mind now clear of her arousal and the odd sensations in her womb began trying to piece together what happened. Suddenly, an animal-like instinct in her head made her push. She felt her muscles contract and a cooling sensation travel down her inner canals taking her rational thoughts away again.
With another contraction she heard and felt a viscous liquid pour out of her marehood and make a gooey splash on the floor. Her breath caught again as another goopy load splashed out of her vagina and plopped onto the ground. The pleasure that had just vacated her mind returned as her muscles finally gave in and stopped trying to close. Twilight moaned as a flow of the goopy liquid poured out of her in a torrent. Her belly slowly shrank as the strange substance oozed out.
Twilight came as the liquid poured out in what felt like a solid stream of jelly, her marecum mixing with the liquid puddling on the ground. She howled in pleasure as her hooves finally touched the ground. Her body, deep in the throes of an orgasm was not ready to hold her though. She collapsed to the ground as the last bit of the goo emptied letting her muscles contract naturally again. Twilight rolled over onto her back gasping for air as she came down from her high. She felt something cold touch her crotch bringing her back to awareness.
Standing in front of the mirror pool stood what must have been around fifty foals made of the same mirror-like liquid as the original figure that made it's way inside her. She realized she had essentially been used for breeding. The adult pony stood between her legs though, it's hoof insistently kneading the tiny nubs above her crotch. The figure melted again before Twilight could wonder why and spread itself over her nipples. The unicorn cooed as her nipples received an impromptu massage in the goo pony's liquid form. This stopped abruptly however as pressure formed again. She arched her back as her nipples felt like they were being stretched. Looking down she noticed she wasn't too far off from the truth. The tiny mounds her nipples sat on started rising as the liquid poured in through the tiny nubs. It wasn't fast or uncomfortable, just odd. Her crotchtits filled like waterballoons as more and more of the goo pony disappeared inside them. The tiny nipples swelled and lengthened on top of the growing mounds. She reached down and squeezed her growing mammaries together, enjoying the sensation.
As the last drop of the pony entered her nipples, she looked up and noticed she couldn't see over the massive mounds she had resting between her legs. Gathering her strength, she tried pulling herself away from the edge of the pond dragging her massive milkers along until a sharp sensation shot through her. She gasped and saw her breasts jiggle like jelly. She stopped pulling herself and decided to see what would happen as another spasm shot through her.
"Wait... If they used me to have children and now they have foals, then what do they want with me now?"
Another spasm caused her boobs to wobble. Twilight panicked again as her previously tiny mounds and nipples rose upwards and outwards visibly filling with more liquid. She stared as they grew beyond the size of a beanbag and went well beyond. The unicorn gasped as she felt a cold mouth grip her nipple and suckle eagerly.
She realized she was being used to make nourishment for the foals she had created. Using her head, she made mental calculations as to how much milk she would need to feed them all.
"N, no! No!" Twilight pleaded.
Her begging fell on deaf ears as gallon after gallon of liquid filled her breasts. She couldn't deny a instinctual satisfaction at filling the belly of hungry foals though. With little choice, she chose to embrace the feeling and kneaded her growing breasts as they grew past the size of weather balloons. Her mind drifted off in contentment as she felt the two foals suckling on her let go, and two more take their place.
Twilight lay on the ground feeling like a proud mother as her mostly normal body recovered from the ordeal. She sat up and saw now fifty or so fully grown pony figures standing over her. The one that had violated her twice now stared at her.
"Wh, what do you want from me now?" Twilight groaned.
The dull eyes of the goo pony flashed and connected to hers.
She experienced, as if from memory, Pinkie Pie's duplication of herself. She saw the Pinkie Pie clones being sent back to the mirror pool. Twilight realized though, that just because they were sent back didn't mean the mirror pool got all of their clones back. Indeed, the excessive cloning thinned their numbers by a large amount. Whereas before there were many voices to converse with, the goo ponies ended up with far fewer causing sadness amongst them.
Twilight felt a pang of guilt rising within her.
"I'm... I'm sorry... I didn't know.
The goo pony's eyes flashed again. This time Twilight felt gratitude filling her heart, and a feeling of terrible regret that they had taken something she could never get back.
"It... It did mean alot to me... But if it means you will have your friends back, then it's worth it." Twilight assured the figure.
The ponies simultaneously smiled what to other ponies might appear to be hollow and dull smiles simply due to their liquid nature, but Twilight could see the sincerity behind them. They hopped in the mirror pool to join their siblings leaving Twilight to recover and glow in the good deed she was able to perform for them.