Author's Notes:

This chapter contains a bit of a bath scene.

It was a beautiful day, and the girls were going for a walk, making fun conversation and laughing at Pinkie's jokes. Outside, they could stand a little closer to Rainbow Dash and not smell her. Ever since her dare with Rarity a few days ago, she had taken to wearing her shorts without her skirt. She had an easier time running like this. Her outfit now had a hint of Rarity's sweat and farts added to its smell, but she barely noticed a difference.

They walked by three girls who looked back and glared at Twilight.

"Aria, Sonata," said Adagio Dazzle. "I believe that is the princess that banished us last year."

"Finally, we can get our revenge," said Aria Blaze.

"I forgot what it's like to be a siren," said Sonata Dusk. "But it's not so bad here. The tacos are delicious!" She farted loudly and giggled while Aria gave her an annoyed look.

...

They spied on Twilight for the rest of the day, knowing they couldn't try anything as long as they were outnumbered. Occasionally one of them would split to pick up food or go to the bathroom. Twilight spent most of the day with her friends. They took note of Twilight's plans to go to the park with Rainbow Dash tomorrow at 10:00.

Finally, they followed Twilight back to her house, and spied on her as she was working on some sort of device.

"Let's get her," said Aria.

"Hold on," said Adagio. "Let's see what she's making first. If it can help us get our revenge, we can steal it and use it against her!"

They waited impatiently as Twilight worked. After about an hour, Twilight's purple shorts darkened, and a puddle formed under the chair where she sat. She continued working on her device as if she didn't even notice. Or maybe she just didn't mind.

Sonata started to laugh, but Aria covered her mouth. "Shut up," she whispered. "You'll give us away!"

But Twilight was so focused on her work that she didn't notice many outside sounds.

"We should have brought a camera," said Aria. "We could humiliate her in front of the whole city."

"We'll keep that option open," said Adagio. "Right now let's see what she's working on."

A few more minutes went by. Twilight let out a loud, wet fart, forcing Adagio and Aria to cover Sonata's mouth again to keep her from laughing.

Finally, she finished her device. She stood up, put it on her wrist, and pressed a button. In a few seconds, she shrunk down to the size of a pen cap. She pressed another button and returned to her original size.

"It worked!" said Twilight. "Now I'd better wash up and go to bed."

She set the device on her work table and walked into the bathroom. Soon, the sirens could hear the sound of the shower running.

"Aria, go in and get it," said Adagio.

Aria climbed in through the window, tiptoed to Twilight's work table, grabbed the device, and climbed back outside.

"With this shrinking device, we can sabotage them in so many ways," said Adagio. "Now, who wants to volunteer to sabotage her first?"

"I will," said Aria. Sonata raised her hand, and then lowered it, looking disappointed.

"Very well. Your first task is a simple one."

...

The following morning, Aria sat on a bench in the park, waiting for Twilight to come. Beside her was a thumbtack, the instrument of her revenge. Aria was wearing her usual white shirt, green vest, and tight purple jeans.

Soon, Twilight and Rainbow Dash came into view, walking towards her on a path. Aria quickly pressed a button on the shrinking device on her wrist, and shrunk down to smaller size. She picked up the tack, which was now half her size, and stood in the middle of the bench, watching Twilight intently as she came closer. She started to feel nervous. She'd have a VERY small window to see which side of the bench Twilight was going to sit on, plant the tack, and get off before she could sit on her.

She was watching Twilight so closely she barely noticed Rainbow Dash.

As Twilight walked by, Aria was ready to make her move. If she stopped and turned when she was by the left side of the bench, that was where Aria would have to put the tack. If she didn't, she'd sit on the right side of the bench. Either way she'd have to move fast. She hoped she wouldn't just walk by the bench altogether.

Twilight reached the left side of the bench, and turned so she was facing away from it. Aria ran to the left side of the bench, set the tack down, then turned around and ran in the opposite direction. Just as she was on the right side of the bench, Rainbow Dash sat on her.

"Ow!" said Twilight, standing up, turning around, and picking the tack up. "Someone put a tack on the bench!"

Rainbow chuckled. "It was a pretty funny prank."

Twilight set the tack on the ground on its side and then sat back down.

Aria was trapped under Rainbow Dash's butt. She was laying on her back, so her face was pressed directly against Rainbow's tush. She could still breathe, but the air was foul down here. Rainbow's butt smelled... really bad. Like she hadn't washed in weeks, maybe months. To make matters worse, her shorts felt dirty and grimy. As if they had weeks' worth of sweat on them and hadn't been washed any more than her.

She couldn't move from where she was, but she could move her arms. She pressed them against Rainbow's butt, trying to make her notice she was sitting on some small creature. Rainbow didn't notice, as she was in conversation with Twilight.

Aria reached for her shrinking device. This would give away her position, but she'd at least be out from under this dirty, foul-smelling rump. She pressed the button, but nothing happened. The device didn't seem to work when she was in an enclosed area that wouldn't accommodate her real size.

Then, Rainbow Dash farted loudly.

BBBBBBBRRRRRRRRRT!

Rainbow chuckled, and Twilight giggled a bit, while Aria took one whiff and gagged. She started pressing her arms and legs against Rainbow's butt, hoping Rainbow would notice and stand up, but she didn't.

"Sorry Twilight," said Rainbow. "I had beans for breakfast."

Aria gulped.

"I don't mind," said Twilight. "I think it's actually pretty funny. And, I am kind of used to your smell."

Rainbow grinned, and let out a louder, deeper-pitched fart.

Aria squirmed harder. Rainbow's farts didn't smell much worse than her butt did on its own, but they made it worse for Aria all the same.

Rainbow Dash's next fart was longer and wetter. Aria started screaming, trying to get Rainbow's attention. But Rainbow couldn't hear her because she and Twilight were laughing. Besides, any sounds she made were muffled under Rainbow's butt.

Next came a boisterous fart. Then, a 7-second, deep-pitched fart. Then, a short but loud fart. Aria was feeling very nauseous.

Then Rainbow Dash let loose with a series of explosive wet farts. It was too much for Aria. Five seconds after she wet her pants, she passed out.

She awoke to the unpleasant feeling and smell of Rainbow Dash's butt pressed against her face. At least Rainbow wasn't farting anymore.

After about another uncomfortable minute, Rainbow Dash and Twilight stood up. Aria pressed the button on her device and returned to her original size before Rainbow could sit on her again. As Twilight and Rainbow were walking way, Aria rolled off the bench on the ground, landing on her back and breathing heavily. The fresh air felt so good.

Twilight and Rainbow heard her and turned around.

"Hey, that's my shrinking device!" said Twilight. "Did you steal it?"

"I wish I hadn't," moaned Aria.

Twilight took the device off Aria's wrist and examined it. "Yep, definitely mine." She sniffed it. "Why does it smell like farts?"

"What's that, now?" said Rainbow Dash.

"I invented a bracelet that can shrink whoever's wearing it by pressing the button. Pressing it again will reverse it. This girl stole it."

"I will have my revenge, Princess Twilight!" said Aria.

"Princess Twilight? No, I'm not a princess. You must have me confused with pony me from Equestria."

"Great... it was all for nothing."

"Rainbow Dash, why don't you discourage her from seeking revenge again?"

"You got it!" Rainbow walked over to Aria's head and turned around.

"Oh no..." said Aria.

Rainbow positioned her rear end directly in front of Aria's face. Aria could smell the foul stench, and slapped Rainbow's butt repeatedly. "Get your stinky ass out of my face!"

"Hey, stop that!" Rainbow sat on Aria's face. Once again Aria's face was pressed against Rainbow's butt, and she couldn't stand it.

Then, Rainbow unleashed another wave of loud farts while Aria kicked her legs screaming.

...

Aria returned to the sirens' house.

"How did it go?" said Adagio.

"Horrible," said Aria.

Adagio sniffed. "Ugh, you smell like farts."

"How many tacos did you eat?" Sonata giggled.

"Shut up," said Aria.

Adagio walked into the bathroom for about a minute. When she returned, she and Sonata grabbed Aria and threw her in the tub fully clothed.

"We're washing this fart smell off you," said Adagio as she and Sonata began scrubbing Aria. "Tell me you at least completed the mission."

"I did, but I think I got the worst of it. I really don't want to talk about it, but if we try anything else like that again, Rainbow Dash will fart on us. And her butt smells REAL BAD even without the farts. Besides, that's not Princess Twilight, it's Twilight from this world."

"Oh." Adagio was disappointed. She'd never have her revenge now.