Trixie smirked, stepping into the enormous, brightly lit grotto. Waterfalls spilled sparkling blue water into deep pools that probably fed into underground rivers. There were gems jutting out from walls and ceilings, and healthy, green grass grew along the floor, flourishing in the sunlight that spilled in from above.
"Maud!" Trixie screeched. "Trixie is here to show you what happens to neigh-sayers!" Her eyes scanned the area carefully, as she knew Maud Pie could hide well in plain sight. Twigs broke underhoof as she took tentative steps forward.
"Hi," came a bland, monotone voice from directly behind her. Trixie shrieked in surprise and jumped. She turned around with a snarl.
"Don't ever scare Trixie like that again!" she demanded, then huffed. "Anyway, like I said, I'm here to teach you a lesson."
Maud tilted her head ever so slightly. "Okay."
"Prepare yourself for my great and powerful cock!" Trixie said, rearing up on her hind legs. A long penis flopped down onto the ground, seemingly having come from nowhere. Maud's only reaction was to aim her eyes downward, followed by a slow blink. Trixie focused on the cock, her eyes narrowing in concentration. Her horn glowed, and a similar glow engulfed the light blue tube of floppy horse flesh making a line across the ground. "Come on... get bigger!"
"That's not how you make one of those bigger," Maud said. "Here, let me help." And, without any change of facial expression, she sat down heavily on Trixie's member.
Trixie screamed.
Maud stared ahead unflinchingly.
The glow around the penis seemed to seep into the gray ass crushing it. Then, the spell fired off just as Trixie's pained scream faded and she took another breath. Maud's rump grew backward and upward, until her ass was like some kind of overinflated balloon.
"What was that?" Maud asked in her standard monotone.
Trixie tried to step back, but her long and floppy cock pulled taut, making her stumble forward and onto the comically large butt in front of her. "Maud! You ruined Trixie's enlargenating spell! It inflated your stupid ass instead. Your stupid, big... sexy... soft and warm... mmmm, oh, that actually feels nice," Trixie said, her length hardening naturally under the big Maud-butt.
"Change me back," Maud said.
"Mmh, but Trixie is enjoying this. And this is what she came here to do anyway. To teach you a lesson for what you said at her show," Trixie said, trying to inject an angry tone into her moaning and breathy voice. "Nopony tells Trixie she can't make a rock disappear. That's—oh, sweet and powerful Trixie, that's good. I-I mean, that's Trixie's business anywa-ha-haaay!"
Maud's wet and surprisingly soft marehood had just winked against Trixie's cock. Maud, unnoticed by Trixie, huffed a little as it happened, and she could not deny that she enjoyed the idea of being filled by a long, hard maredick. "Okay," she said. "Fuck me, then."
Trixie was surprised by the quick change of heart, but didn't show it. Instead, she smirked, convincing herself that she knew this was how it was going to happen all along. As soon as Maud stood up, Trixie's cock, covered in smushed green grass and some dirt, sprung free, and all eighty Equestrian Measurement Units (EMUs) of it jutted forward below her.
Wordlessly, Trixie slid the tip of her giant futacock against the enlarged ass of Maud, slipping it between the two fuzzy cheeks and running it back and forth across the ponut hidden within. She pulled back, using her magic to line her cock up with a wet spot that seemed to be a likely location of the earth pony's marehood, and then thrust forward.
"Haa-oww!" Trixie said as her penis was roughly stopped, bending it painfully. "Maud, your ass is too big, and I can't see your pussy. Help me out, here!"
Maud wiggled her rear, and the wide tip of Trixie's erection found a gloriously warm and wet entrance, eliciting a moan from her. "By the way, Trixie," Maud said with a short pause as she slowly pressed back, burying the cock inside her, "I can crush rocks with kegels."
Trixie's heart nearly stopped. With her sensitive and vulnerable flesh buried inside what might as well be a trap for an ursa major, she felt the urge to pull out and run away. "But you can be gentle too, right?"
Maud only smirked.
Sudden pressure pressed Trixie's flesh rod from all sides, and she cried out in surprise, a cry that quickly became a lewd and growling moan. She pressed forward despite her worries. Maud wouldn't really hurt her, after all, right?
The squeezing diminished, and Trixie found Maud to be a wonderfully tight but accommodating lay. Gripped but no longer crushed, Trixie found it relatively easy to slide along the tight folds of Maud.
"Ah! Maud! That f-feels... amazing!" Trixie said. She thrust deep into Maud, leaning over and hugging the inflated pony ass below her, noting that it was a good size for cuddle-fucking. Huggable and large, but not ridiculously so.
Trixie found herself near her limit, as the constant assault of tight passage against stiff and eager meat continued.
"Trixie is... is going to cum!" Trixie announced.
"Me too," Maud said flatly.
Trixie's wide tip throbbed and flared as she orgasmed. Sparks, tiny firewofks, and confetti exploded from her tip, pelting the insides of Maud with burning heat and wet bits of colorful paper. The horny showmare writhed and moaned as she came, clinging to the beloved ass beneath her like a rock in a hurricane. She had never had such an amazing orgasm in her life, and in the back of her mind, filed the sex away as the first time it was better than masturbation.
Maud came too. Her ponetang winked wildly and squelched as marecum leaked from it. She blinked slowly.
As soon as Trixie was spent, she slid back and fell over, panting.
"That was... wow... I... I mean, the Great and Powerful Trixie enjoyed that," Trixie said.
"Yeah," Maud replied. "Can you fix my butt now?"
"Oh, that. It'll wear off in about fifteen Equestrian Time Units."
"Oh. Okay."
"Until then, wanna cuddle?" Trixie asked.
"Sure," Maud replied, and she dragged her ass over to Trixie to lie down with her.
The two ponies fell asleep in each other's hooves, and were later woken up by Mudbriar. He got angry at Maud, but only because Trixie had stepped on a stick he liked while she was entering the cavern.
