Author's Notes:

Just something I thought of last minute despite my writer's block for everything else. This will be ponies. I've been fantasizing about Twilight more lately and I think this will finally satisfy that.

Sorry if it seems a bit rushed. Pure fetish fuel as usual, but that's what the "Porn" genre is for.

Might not write again for a while after, and I hope this can be like a "finale", at least for now. And again, if you find this kind of thing disgusting - as anyone without the fetish quite understandably does - please ignore it.

Pinkie Pie had just perfected a new type of powder she'd have fun pranking ponies with. With a combination of fart powder, dried prunes, and a few other ingredients she'd experimented with, she was able to make a powder that made anyone who ate a small amount of it have to pee and poop really badly, as well as making them gassy.

She had tried it, immediately feeling its effects and rushing to the toilet, enjoying the relief and giggling at her flatulence.

Now that she had this done, it was time to use it for pranks.

...

Rainbow Dash was playing volleyball against Applejack, both wearing a yellow tank top and skintight white shorts.

Pinkie thought Rainbow would appreciate this first.

"Cider?" Pinkie held out a mug of cider that had been stacked at the side.

Rainbow Dash and Applejack were both dripping with sweat. So, they decided to take a short break and have a refreshing drink. Pinkie gave one mug each to Rainbow Dash and Applejack.

She had spiked Rainbow's cider with a teaspoon of that powder.

Only seconds after Rainbow and Applejack returned to their game, Rainbow's stomach grumbled uncomfortably. She crossed her legs, let out a few farts, and then, sweating even more, she ran into the nearest outhouse.

A series of wet farts could be heard on the other side of the door. Then, after many flushes, Rainbow walked out, looking very relieved.

"I used up all the toilet paper," said Rainbow, "so my butt might be a little dirty. Also, I may have leaked a bit before I got my shorts down, but you can't tell cause they're soaking wet anyway."

Pinkie Pie fell on her back laughing.

"Did you put something in my cider?" Rainbow said.

"I invented a new powder that did all that to you, and I'd say it works just fine!"

Rainbow laughed. "Good one Pinkie Pie! You'll have to give me a box of that powder sometime."

"Good idea!"

As Rainbow and Applejack continued their game, Pinkie bounced away to find more ponies to prank. She wouldn't dare use this on Fluttershy... but it would be really funny using it on Rarity!

...

Rarity was just exiting the stage after a fashion show, wearing a pink dress with a light blue pair of panties underneath.

"Hey Rarity!" said Pinkie. "Want a cupcake?"

"I suppose... if the icing doesn't stain."

"It won't."

Rarity ate the cupcake, which Pinkie had sprinkled her powder on the top of.

Soon, Rarity felt its effects. She frantically looked around and, noticing a restaurant, ran into its bathroom, farting the entire way while Pinkie giggled.

Rarity exited the bathroom, red in the face because the pony in the next stall had heard her fart, and smelling a little, for she had accidentally let a little bit out before getting her panties down.

"I'm so sorry you had to see that," said Rarity. "Something I ate must not have agreed with me."

"It could happen to anyone," said Pinkie, and she bounced away.

...

Pinkie got two hay burgers. She put a small teaspoon of powder on one, and, getting a little curious, sprinkled about half the box on the other, deciding to eat it after her next prank and see how it affected her. She had a feeling she was going to like it.

She found Twilight Sparkle at her castle. Twilight had just been running a race with Starlight Glimmer so she wore a dark blue T-shirt and skintight red shorts which were damp with sweat.

"Hey Twilight, want a hay burger?" said Pinkie.

"I'd love to," said Twilight. She levitated one of the burgers and ate it rather quickly.

Pinkie froze. Twilight had eaten the burger that had excessive amounts of powder on it, the one Pinkie had intended for herself.

"What's wrong?" said Twilight.

Suddenly, she felt its effects, feeling an intense urge to pee and poop.

"Urgh... I'll be right-"

PPPPPPPPPPPBBBBBBLLLLLLLLLLRRRRRRRRT!

Twilight blushed as she released a foul-smelling mess into her shorts, while at the same time she began peeing. It wasn't the first time she had soiled herself, but it was still embarrassing.

Finally, she stopped messing herself, but kept peeing, soaking the crotch and legs of her skintight shorts. She let out a few more wet farts, but then the next fart turned into a continuous log of manure that continued to make its way out of her despite her attempt to stop it. She moaned in embarrassment and discomfort.

Spike started to laugh hard while Pinkie just giggled nervously, feeling bad for Twilight.

Twilight stood still as she finished messing herself again, still peeing. She let out some more boisterous farts, ranging from one second to five, and then, without warning, the third wave came. Hyperscat filled her already heavily-soiled shorts, and began to leak through her leg holes, oozing down her legs along with the pee that was still splashing to the ground and forming a big puddle that had reached Pinkie's hooves.

After that, Twilight farted loudly four more times, and then, diarrhea exploded out of her rear, adding to the tremendous mess in her shorts and dripping down to the ground behind her.

Twilight finished peeing, and then finished pooping again. She paused, bracing herself for the fifth wave, but it didn't come. She farted again, and was just about to relax, when she suddenly let out another boisterous fart that released a little more scat into her shorts. Then came another wet fart, and she was done.

"I'm so so sorry Twilight," said Pinkie. "I didn't mean for you to get that burger. I wanted to experiment with it myself. You were only supposed to get one that would make you have to go really badly but have enough time to get to a bathroom."

Twilight continued to stand still, shocked at how much she had soiled herself, even more so than the gala incident.

"Phew," said Spike, holding his nose. "You smell awful, Twilight!"

He was absolutely right, for she smelled of farts, urine, and manure, especially her shorts, which were overflowing with her mess. She didn't even attempt to deny it, as she took a whiff of the air around her and cringed.

"I'll start a bath for you," said Pinkie.

Twilight followed Pinkie into the bathroom, leaving a trail of messy hoofprints behind her.

They didn't bother trying to wash her outfit, for it had been damaged beyond repair and had to be thrown out.

It took a while to wash Twilight completely (Pinkie scrubbed her butt extra hard), and Pinkie threw a really big party for her to make up for causing her accident in the first place, with her and Spike promising never to tell anyone. By the end of the party, Twilight was over it.