"Now, let's see if I've memorised this pattern thoroughly." Doctor Whooves darted throughout his laboratory with a parchment in his mouth. Today, he had a hunch that he was going to make a new breakthrough with his inventions. "Boiled mercury added to this batch of perfectly defrosted Equinite, plus a pinch of sodium chloride should give me the perfect textures for this new potion..."

Doctor Whooves gently placed each and every ingredient into a potion bottle and attached it to some apparatus, distilling it on a heated plate with fire burning in the patch beneath it. The mixture inside the original vial half-vanished into steam that travelled through one pipeline, with the other half being slurped up into another path of pipes and through a number of other glass bottles and canisters.

"Perfect." Doctor Whooves watched as his new concoction dripped into a small test tube. He then picked it up and applied it to a lone potion at the other end of the room in small bursts. "Now then. Easy does it..."

"DOCTOR!" Derpy Whooves came bursting through the front door, making him jump and spill the contents of the test tube into the big potion, causing it to fizz up and explode in his face, making his mane burst out in all directions. "Oh. Am I interrupting anything?"

"Well" —he turned around to face Derpy, fixing up his mane as he did so— "If you consider making me leap in surprise, allowing me to make a mess of a potion that I had spent all morning trying to create, then yes. You are interrupting something, miss Hooves." He gruffly crossed his forelegs.

"Oh. I'm sorry." Derpy hung her head and looked at Doctor Whooves' ash-covered face. "I-I could just leave this parcel here I-If you want."

"Parcel?" Doctor Whooves tilted his head and looked at Derpy's delivery bag. Sure enough, there was a large rectangular package addressed for him. "Is that my new Photon Synthesizer?"

"Photo what now?" Derpy squinted her eyes as she pulled the package out and read the contents carefully. "I don't know what it is myself, but I do know that it's for you, Doctor." She plucked it out of her bag and gently set it down by the nearest table. "Glad I could help!" She saluted and gave an innocent smile.

"Now this is a right find, I think." Doctor Whooves eagerly ripped the packaging open, showing off a metallic device with many bright flashing lights around it, either in strips or flashing buttons. "Harnessing the power of pure daylight, this Photon Synthesizer could work wonders in many of my experiments."

"Ooh. Sounds pretty." Derpy watched as Doctor Whooves turned the machine on and pulled on a chain, causing the roof above him to open up and reveal a glass skylight.

"Now then. It needs a bit of a preliminary charge up before it starts working, according to the pony I purchased this from." Doctor Whooves set the device beneath the light and left it alone. "Once everything is set up, we're good to go for some splendiferous light-based experiments. My mind is flooded with possibilities for how this could benefit the ponies of Ponyville!"

"Is there anything I could do to help with your new protein syndicate whatchamacallit?" Derpy asked, flitting closer towards it. "I'm really good at helping ponies out."

"Derpy, my dear. As much as I appreciate your assistance, I don't think I need to remind you about what happened the last time you helped me out with one of my experiments." Doctor Whooves rolled his eyes.

"That wasn't my fault!" Derpy pouted and stomped the ground. "I had no idea that there was gonna be a pancake festival outside. All that sticky gunk really messed up my wings and broke the part you sent me to deliver."

"Well, either way, I'm still a bit on the fence on whether or not you'd actually be able to help me." Doctor Whooves tilted his head at Derpy. "Now, don't get me wrong, miss Hooves, you're a great friend to have. But when we're in the laboratory, perfection is absolutely critical. One mistake could lead to another, building up like a pressure cooker. Disaster upon disaster, calamity on top of calamity, until BOOM! Everything goes wrong and Ponyville's plagued with a scientific mishap that I created because of a little accident!"

"Aw, c'mon, doc. Just give me a chance." Derpy fluttered her eyelids. "I'm sure I could help you out in some way."

"It's a nice offer, Derpy, but I'm afraid that I'll have to decline." Doctor Whooves shook his head. "I'm far too backed up as it is. Now that the potion I've been making has gone kaput, I'll need to spend the whole day getting all the ingredients to properly prepare another one."

"Well, can I go and get those ingredients for you?" Derpy asked. "I'm a master in getting things for other ponies."

"Derpy. The stuff I need is very complex. I don't think you'd even be able to figure out what half of the stuff I need is." Doctor Whooves frisked his lab while speaking. "If anything, I worry that you would decide to wing it if you didn't know what I wanted. And then, we know where that would get us, right?"

"I'm sure I'd be able to work with it." Derpy smiled. "I've been around your lab a lot, Doctor. I think I'm beginning to get the hand of this science-y stuff." She eventually came over towards a small test tube with a bright pink liquid inside. "Ooh! Is that pink lemonade? I love that stuff!"

"Derpy. Please don't eat that." Doctor Whooves waved his leg as he set up his new Photon Synthesizer and let it bathe in the sunlight. "I've been experimenting with that phial for over a month now. The composition is very unstable at the moment. If you drink that stuff, who knows what could happen?"

"You worry too much, Doctor. I know pink lemonade when I see it." She took the potion from the holder, uncorked it, and began to gulp the mixture down.

"Derpy, DON'T!" Doctor Whooves turned around to see Derpy drinking the potion. He made a quick dash towards her and tried to snatch the potion away, but by the time he touched the glass, the mixture was completely gone.

"Mmm..." Derpy smacked her lips together once the potion trickled down her throat. "Yummy!"

"Derpy, what's the one thing I asked you not to do?" Doctor Whooves slapped his hoof against his face.

"Drink the potion?" Derpy responded.

"And then what did you do?" He folded his hooves.

"Drink the potion." She put the phial back where it sat.

Well, this might be worth a bit of examination... He thought to himself as he watched Derpy's eyes drift around the room. "Derpy, how do you feel?" He asked. "Any pain? Irregularities? Need to pass wind or belch a lot?"

"Nope!" She smiled. "That was the tastiest drink I ever—" As if the timing couldn't have been more perfect, a sharp pain was felt in Derpy's chest, as if she had been stabbed through the heart by something "—Gah! OK, now it's bad..."

Derpy's entire body began to jiggle and vibrate as the potion's contents began to take their toll on her. She felt her body stretch and retract rapidly as she grit her teeth together and collapsed to the floor, holding her hooves to her belly as she writhed around like a fish that had been plucked from the sea. She let out a large groan as she twisted onto her back and heard a large hissing noise, as if someone was blowing air into a balloon.

"Derpy? Whatever is happening to you?" Doctor Whooves could only look on and watch as his friend suffered before his eyes.

Suddenly, Derpy's body began to bulge outwards. Her belly began growing in size at a rapid pace before her body became bloated and flabby. Every part of her body, apart from her hair, head, and neck, were beginning to inflate bigger and bigger, as if she was a zeppelin. Because she was growing in size, she ended up unintentionally knocking over most of Doctor Whooves' equipment, making it shatter on the ground as she continued to plump up in size.

"What's happening to me?" Derpy asked as her neck and head shrunk backwards into her body until only her face and mane was visible.

"It might be a case of sudden excess trapped wind. Hold still for a second. I'm going to try and jump onto you and squeeze the air out before you turn into an airship." He limbered up for a dash then ran forward at the massive Derpy, leaping onto her back to try and fix her up with a simple smash, but with no effect. "Huh. I was sure that was going to work..." Before he could say anything else, his entire body was pressed against the roof. He was sandwiched between his house and the still-inflating Derpy.

"Doctor! What's going on?" Derpy tried to wiggle her hooves around, but she couldn't. As she tried to look around for an explanation why, her body began to rupture the walls around Doctor Whooves' laboratory. "Why aren't you speaking?" She heard a few faint mumbles, but she couldn't make anything out of it when it was coupled with the noise of crumbling wood and cracking glass.

Eventually, the house around them broke completely and both Derpy and Doctor Whooves were carried into the air. The roof that she had collected on her travels slid off of her body and fell into the laboratory, where it destroyed the rest of the equipment below. And even as they were out in the open sky, Derpy was still getting bigger. She had gotten so large that her Cutie Mark could be seen by the ponies of Canterlot—and they lived on a mountain far away.

"Doctor. I'm really, REALLY sorry about what happened to your house..." Derpy looked down at the desecrated pile of rubble that used to be his house. "If you want, I could send a message to Princess Twilight about this. She's good with helping ponies out."

"No. No. No. N.O. That means no, Derpy!" Doctor Whooves shook off the dust and whatever glass he had collected on his ride on her back. "Whatever that potion did to you, you've completely wrecked my house! I spent years gathering all of that data and knowledge, and now you've ended up destroying my life's work in a single swoop!"

"It's not all bad, Doctor. Look." Her eyes drifted down towards a single piece of machinery within the wreckage. "Your pro thong sing the scissor is still there."

"It's called a Photon Synthesizer, Derpy." He slid down her bulging body and had to hold on tightly to her flabby body to avoid sliding over her and falling to the ground. "And besides, it won't mean anything without the rest of the gadgets I had to create in order to perform my experiments anyways. It might as well just be made out of ice-cream now!"

"Oh..." Derpy drooped her eyelids and sighed.

"But let's not focus on that for the time being. I think the more pressing matter now is WHAT IN PRINCESS CELESTIA'S NAME HAPPENED TO YOU?" He clambered back up to the top, wiggling his legs as he tried to inch onto the top of Derpy's massive body. "In what world are you able to drink a highly dangerous potion and turn yourself into an inflatable pony? It makes no sense! The scientific ramifications of this whole thing are absurd as they are clever!"

"This isn't the time for science, Doctor. Look at me!" Derpy waved the little stumps that used to be her hooves. "I'm as big as Twilight's castle! And I don't even look half as sparkly as it does..."

"Oh, I don't think that's entirely true, Derpy." Doctor Whooves looked around her body to try and find anything that he could compliment her on. "You... have a rather nice sheen on your bulbous figure now. Th-that's a good thing. Not a bad thing."

"You think I'm ugly because I'm fat, right? Admit it." Derpy sniffled a little bit as she felt the folds of her zeppelin-like body squash the sides of her face. "You don't wanna hurt my feelings because you're smart, while I'm just a bubble-brained dunce."

"No! No! It's nothing like that, really, Derpy." Doctor Whooves waved his hooves in front of his face as fast as he could, shaking his head. "I think you're a great pony, Derpy."

"No, you don't." Derpy sighed. "I heard what you said back down there. You don't want me to help. You just want me to be the delivery pony. I should just float off and leave you alone."

"Derpy! You know that I don't hate you. I'm just very busy with my research every time you just come around to visit. I'm not going to call it bad timing, because I know that'll just make you feel even sadder. Ugh! I just don't know what to say or do about this whole thing! I'm so flustered because of how sudden this whole thing is!" He raised his hooves to his temples and rubbed them vigorously as he tapped his foot against her body. "Look. Derpy, can we just leave this issue until later? I feel a bit of a headache coming on from this whole balloon-ified you situation..."

"Well. The sooner you turn me back into normal, the sooner I can leave you alone with your throw con swim the side stir..." Derpy let a small fart slip out of her butt, which propelled forward through the air a short distance.

"I'm sure that one of the princesses will see this whole thing and fix it in a snap. But until then, all that we can do is wait." Doctor Whooves sat down and looked at the clouds around him and Derpy. "As much as I would like to fix this whole thing personally to make up for how you feel, I'm not sure how I'm going to get all of that excess air out of your body without causing you harm. I mean, I could give you a powerful kick, but I think that'd just hurt you instead of fix you."

"What about her?" Derpy looked out towards a blue blur streaking through the sky. "I'm sure that the pegasus over there'd be glad to fix me up."

"Wait, what?!" Doctor Whooves rapidly jumped onto his feet and wobbled over towards Derpy's head, where he saw Rainbow Dash shooting through the air towards them. It didn't take her long to make it to both of them, and she flapped her wings backwards to avoid crashing into them.

"Hey. What happened here?" Rainbow Dash looked down at Derpy, before looking up at Doctor Whooves. "Do you think you could explain?"

"Miss Dash! Oh, I couldn't be happier to see you on a day like this." Doctor Whooves beamed at Rainbow and slid his hooves over Derpy's body. "As you can see, we're in a bit of a pickle here. Miss Hooves swallowed one of my potions and plumped up in seconds. I'm not entirely sure on how it happened myself, but I do know that we require someone's help to fix this mess."

"And fast. I don't wanna stay like this forever!" Derpy tried to flap her wings, but she couldn't move them an inch. "I can't feel the rest of my body anymore."

"Hey. Don't worry about it." Rainbow Dash waved her hoof idly. "I'm sure that all that air's gonna come right outta you with a little bit of force. You two don't mind if I give her a little kick, do you?"

"How little?" Doctor Whooves lifted a brow.

"One fixed Derpy, comin' up!" Rainbow Dash flew underneath Doctor Whooves and Derpy, landed on the ground, and looked up at her inflated stomach. I'm sure they'll be thanking me for this later. Chalk another win up for Rainbow Dash. She squatted down, unfurled her wings, and launched into the air like a rocket ship at Derpy's chest, leaving behind a trail of clouds as she climbed.

"Miss Dash? I don't think that much force is ne" —Before he could finish, Derpy was hit by Rainbow Dash and carried higher into the air, taking Doctor Whooves with her— "cessary!"

"Whoooooaaaaa!" Derpy cried as she felt the wind forcibly shut her eyes as she was launched high into the strastosphere by Rainbow Dash's kick. "Doctooooooor! Do somethiiiiiing!"

"I'm trying to!" Doctor Whooves felt gravity playing against him as his face pushed against Derpy's flesh. He tried to move, but he couldn't even wriggle an inch given how fast she was rising.

"Now for the finishing touch!" Rainbow Dash swooped ahead of Derpy and Doctor Whooves, creating a slipstream as she swooped past them. She travelled so fast that she created a Sonic Rainboom, which not only knocked the two ponies away, but also caused Derpy to spin away. "You two better hold on to something, because this is gonna be a big one!" Rainbow created a massive rainbow in the sky before swooping down towards Derpy and Doctor Whooves. With incredible force, she crashed straight into them, cannonballing them towards Twilight's castle.

Derpy spiralled out of control and watched the whole world spin around her. Now she knew just how the laundry felt when it was put through the washing machine. Before she could even re-orient herself, she smashed into Twilight's castle, throwing Doctor Whooves off of her and straight through the balcony door, where he span and rolled down the corridors before he landed right in front of Twilight Sparkle and Spike, who were both submerged underneath a massive pile of books.

"Doctor? What's going on here?" Twilight burst out of the pile with her magic, hastily putting the books away. "I heard a loud crash, then you just came in."

"Have you met the prench?" Doctor Whooves stumbled around, his eyes rolling around in his head as he tried to snap back to reality. "My... GOD! They know how to party!"

"Well, look at what the cat dragged in, eh?" Spike brushed his quills down and watched Doctor Whooves shake himself out of his trance. "If it isn't the oncoming storm himself, Doctor Whooves."

"Wait. Where's Derpy?! Oh, sweet Celestia, is she OK?!" His eyes darted around the room, trying to find any sign of Derpy Whooves anywhere. "Oh no. Oh no..."

"Slow down, Doctor. You look like you've been in a rather bad accident." Twilight walked over to Doctor Whooves and used her magic to lift up a blanket and pillow. She then escorted him over towards the bench and helped him sit down in it. "Now, can you tell me what happened?"

"Well, it started when Derpy delivered my package. She wanted to try and help me out in some way, so she decided to eat one of my highly uncontrollable potions," he started. "When she did, she turned into a massive airship pony and jut floated higher and higher into the air. We thought that Rainbow Dash would be able to help us, but she decided to try and kick the hot air out of Derpy's body to turn her back to normal. And because of that, we were sent crashing into your castle."

Twilight and Spike could only stare at him slack-jawed, blinking as they took the whole story in.

"Well... uh, I'd be glad to help you out, Doctor." Twilight was the first one to break the silence and walked over towards the balcony where he had come in from. "If Derpy really is a massive balloon pony now, we should do all that we can to turn her back to normal."

"Uh, Twilight? Am I the only one who thinks that this whole story is just a load of hooey?" Spike climbed Twilight's legs and hopped on her back, holding on to her neck as she trotted off. "I mean, what if he's still shaken up by the crash? He might've been given some kind of amnesia or something!"

"Spike. I'm not entirely sure about the whole thing myself, but would a Doctor Whooves who flew straight into the castle like a cannonball be lying to us?" She asked.

"Uh..." Spike tapped his foot rapidly as he brought his claw to his chin.

"Exactly." Twilight walked over to the balcony. "He might still be shaken up, he might be telling the truth, but whatever the case, something shook the castle up, and I'm not waiting around for more answers. If something was able to cause that much damage to the castle with a single hit, then we should take care of it straight away."

When Twilight got outside, she heard a loud groaning noise coming from beneath the balcony. She went over the edge and fluttered down to see what it was. She could already see Derpy's cutie mark, so she flew up towards her face and watched as it sank even further into her body.

"Y'know... Now that I think about it, I want to be a balloon forever..." Derpy stuck her tongue out as she saw stars dancing above her head. "I'm sure that I'd love to fly high into the air, with my tail as the string for some giant pony or monster to play with..."

"Derpy. Wake up." Twilight let a small stream of magic seep into Derpy's mouth, where it swirled around her head and made her eyes glow briefly "Are you alright?"

"Princess Twilight!" Derpy's eyes lit up again, but this time, they didn't turn into bright spotlights. "Oh, thank Celestia. If there's anypony that can fix me now, it's you!"

"I suppose that I should. Given that a certain somepony almost ended up wrecking the place..." Twilight grumbled and looked out towards Rainbow Dash, who went off to clear away the clouds. "Now, just hold still. This shouldn't hurt at all."

"Please hurry, Twilight. I feel myself getting bigger and bigger every second..." When Derpy finished her sentence, her entire head shrunk into her body and she was getting so big that it was beginning to uproot the castle.

Twilight quickly opened her wings up and lit up her horn again. She took in a lot of magic before unleashing it at Derpy's chest, causing a series of white ripples to spread out across her entire body. With another surge from Twilight, the beam got stronger, encasing Derpy in a powerful pink bubble of magical energy.

As Derpy felt the magic swirl and cocoon her body, she felt the air inside of her begin to rumble and ferment. She puffed out her cheeks and let out the largest burp and fart that she could, causing her once puffy body to shrink down. As she got rid of the wind, she started to feel her hooves again, followed by her wings, and eventually, the rest of her body. Once she let out all of the air, she was back to her normal size, trapped inside a cloud of the gas that she had let out.

"There we go. Now doesn't that feel better?" Twilight popped the magical bubble around Derpy, causing all of the air around her to dissipate and fly off in all directions.

Once Derpy was back on her feet, she gave herself a quick sniff and reviled. "Yuck! Why do I smell like this?"

"Don't worry too much about it." Twilight smiled and gave Derpy a gentle rub on the head. "Now, where's Doctor Whooves?"

"Derpy?! Derpy! Where are you?" Doctor Whooves was running around the foyer, sweat running down his forehead as he looked down each corridor. "Please, answer me!"

"I'm here, Doctor!" Derpy flapped her wings and darted into the foyer, tackling Doctor Whooves and pinning him to the ground. "Did you miss me?"

"Oh, I certainly did, Derpy." Doctor Whooves' fear washed away into a grin instantly once he picked himself up from Derpy's dash. "I'm glad to see that you're still alive and not a balloon anymore."

"I'm glad of that too, Doctor! And I've learned my lesson." She squinted her eyes and gently nuzzled Doctor Whooves' neck. "I promise that I'll never, ever, EVER try and drink the lemonade you make in your lab ever again, Doctor. It's too weird and doesn't do much for me."

"A very important lesson to learn, my dear." He nodded. "And, I guess that I owe you an apology for how stubborn I was. I had just been caught behind with so much stuff that I didn't really have the time to spend with you. If I had just been a bit more open with myself and let you help me out, then we wouldn't have had that little incident today."

"It's alright, Doctor. None of us knew what was going to happen with that lemonade." Derpy cooed and gave Doctor Whooves some breathing room. "Now, I can go back to my job of delivering stuff to the ponies of Ponyville."

"But first, I think you need a shower, my dear." Doctor Whooves pinched his nose and tried to waft the stench Derpy was emitting away. "Phwoar! It's like you've been dragged through mud and skunks!"

"I know, right? It's like I've been hit by the stinkiest smell in Equestria!" Derpy giggled. "Anyway, I think I'd better let you get back to work, Doctor. Many more ponies to see before the day's done, and I'm horribly behind schedule! Bye!" She took to the skies and dashed off.

"Take care, Derpy!" Doctor Whooves waved her off before leaving the castle himself. "Thank you for this, Twilight. But, uh, if I may, do you think that I could ask you for some more help?"

"Oh?" Twilight lifted an eyebrow. "What is it now, Doctor?"

Doctor Whooves led Twilight towards the wreckage of his former house. The ground had been peppered with bits of wood, plaster, and various other housing materials, while the remains of the laboratory was in even worse shape, with nothing more than a hollowed out square of land, with lots of wrecked science equipment scattered around.

"Oh my..." Twilight looked at the ruins of Doctor Whooves' house. "And you say that Derpy drinking one potion did all of this?"

"Yes. What a crazy thing science is, huh?" He chuckled and walked up to his Photon Synthesizer. "At least this thing's still intact. I don't know what I could've done without it." He gave it a gentle tap, only to watch it fall apart and sprinkle around his feet. His forehead twitched as he threw his head to the sky and screamed, "DERPY!"

Author's Notes:

I want to give a big thank you to the Castaway Pariah for coming up with the idea for this story. This story is living proof that commissioning me can work, given the chance. Because I know the last time I did a commission, things got a bit hairy with the guy who originally came up with the idea. I hope that this story gives you hope. And remember; if you want a story written by me personally for you, then just send me some dough through Paypal or post, and I'll get to work as fast as I can.

Have a nice day!