Author's Note: Please use Mountain Dew responsibly.
Inside the Ponyville library, Twilight Sparkle was going through the cabinets, trying to collect all the ingredients she needed for a complicated potion. Her search was not going well, because she kept being distracted by her talkative dragon assistant.
"How much longer do you think it'll be?" Spike asked.
"I don't know, Spike," Twilight Sparkle responded.
Spike twisted his head around so he could double-check his back. "But all of the other dragons have wings. Why haven't my wings started growing yet?"
"For the last time, I'm not an expert on dragon anatomy," Twilight said, using her magic to move some unnecessary things aside.
"But I wanna fly!" Spike said. "Rainbow Dash is always bragging about how cool flying is, and dragons are supposed to be the best flyers ever!"
Twilight stopped rummaging through the cabinet and turned around, with a slightly annoyed look on her face. "Do you really want to fly?" she asked.
"Sure!" Spike said. "I mean—"
Twilight used her magic to levitate Spike into the air.
"Woah, wait!" Spike said. "That's not—"
Twilight began to move Spike in a large circle, around the library. When she started moving him faster and faster, his stubby arms and legs began to flail about.
"STOP! STOOOOP! I think I'm going to be sick!" Spike screamed.
Twilight chuckled to herself, then let Spike down gently.
"That's what flying is like!" Twilight said happily.
Spike's eyes were rolling in all directions, until Spike shook his head and reoriented himself. "Hey, why'd you stop?" he asked. "That was kind of fun! Think we could try it outside next time?"
Twilight Sparkle sighed. So much for getting Spike to forget about flying.
"Spike," Twilight said. "I'm trying to make a potion here, but you keep distracting me!"
"Oh," Spike said. "Sorry about that. Why are you making a potion?"
"It's for the princess," Twilight said. "She wants me to make a new type of Mountain Dew."
"Mountain Who?" Spike asked.
"Mountain Dew, Spike," Twilight said exasperatedly. "It's an energy drink for unicorns."
"Oh," Spike said. The only energy drink he knew about was Red Bull, which pegasi use to help their wings.
"Mountain Dew increases a unicorn's magical abilities, but only for about ten minutes," Twilight lectured. "The Princess is hoping I can create a variation that lasts longer."
Spike thought about this for a moment. "Hey, that'd be great!" he said. "If you could invent a better magic potion, everypony would want it! You'd become the world's most famous unicorn!"
"Students taking final exams at the magic academy would love it, that's for sure," Twilight said. "But I'm not sure I can succeed. I've never tried Mountain Dew before, and I'm not very good with potions."
"Ah, you can do it!" Spike said. "You're Celestia's star pupil! You can do anything!"
"Thanks, Spike," Twilight Sparkle said, nuzzling her little assistant lovingly. "But this is a tough assignment. If I'm going to make a potion that's super-charged with magic, I need to get my hooves on the most powerful force in all of Equestria."
"The Elements of Harmony?" Spike guessed.
"Nope," Twilight said. "Something even stronger than that."
"The magic of friendship?" Spike asked.
"Guess again," Twilight said. "What's the one thing you know that absolutely cannot be stopped under any circumstances?"
"Pinkie Pie on a mission," Spike said.
"Exactly," Twilight said. "If we could harness some of Pinkie Pie's natural energy, we could make the greatest Mountain Dew ever."
Thirty minutes later, Pinkie joined Twilight and Spike in the library.
"I love baking!" Pinkie Pie said, jumping up and down. "Are we going to make cupcakes? They're delicious!"
"We're not baking food," Twilight Sparkle explained. "We're making potions. It's a completely different—"
Pinkie Pie started singing the cupcakes song, much to Twilight Sparkle's irritation.
"Pinkie! Hold still for a moment!" Twilight ordered.
After some doing, Twilight managed to levitate a metallic helmet on top of Pinkie Pie's head. Wires went from the helmet to a small handheld machine that Spike was holding. The machine looked sort of like a battery.
Pinkie stopped jumping around and stood still. "What's this machine do?" she asked.
"It's designed to collect your excess energy," Twilight said. "Now, whenever you do something, the helmet will transfer it into my machine."
"Oh," Pinkie said simply. She kept standing in place for a moment, then scratched one of her legs with her hoof.
"...So?" Twilight said.
"So what?" Pinkie asked.
"So, aren't you going to jump around and be loud?" Twilight asked. "I can't harvest your energy if you're not expending any!"
"Hmmm...nope," Pinkie said, shaking her head slightly.
"But the machine doesn't work unless you're giving off a lot of energy!" Twilight said. "Come on, where's the high-energy party pony we all know and love?"
Pinkie shrugged. "I'm kind of tired today," she admitted.
Twilight sighed. "Look, if you help me out here, I'll buy you some candy, okay?" she asked.
"CANDY?" Pinkie gasped loudly. "CANDY CANDY CANDY! IT'S DELICIOUS AND DANDY!" she half-shouted, half-sang as she danced around the room.
"Twi—Twilight?" Spike asked. He struggled to keep his grip on the energy collecting device. "What's wrong with this thing?"
Twilight looked over his shoulder and gasped. Pinkie Pie's power level was over 9,000! "It's overloading!" Twilight said. "Quick! Disconnect it before—"
KABLAM!
The device exploded into twenty pieces, and Spike was sent flying across the room where he slammed into a bookshelf.
"Uh oh," Twilight said.
"Oh no!" Pinkie said, stopping her song. "Spike, are you okay?"
"I'm...fine..." Spike moaned.
Twilight sighed. "Thanks for the help, Pinkie, but I think that was a bit too much energy," she said.
"I still get my candy, right?" Pinkie asked. "Right? Rightrightrightrightright?"
"Ugh..." Spike groaned in pain.
The brave and resourceful Twilight Sparkle did not let one failure get her down. No, she decided to go back out there and try again!
Seven failures later, though, Twilight was beginning to think she should call it quits.
Rainbow Dash accidentally dropped the energy-collecting device in a lake when she was flying around. Applejack's powerful tree-kicking legs smashed the device in half. And Fluttershy's loudest screams weren't even enough to register on the energy-collecting device.
"I've asked everypony I know!" Twilight complained, pacing back and forth in the library. "What else can I do?"
"I dunno," Spike said. "Maybe you should experiment with something else."
"I can't!" Twilight said. "Princess Celestia herself asked me to perform this experiment! I can't let her down!"
"Twilight..."
"But I can't make Mountain Dew, until I get a large source of energy! What am I supposed to do, hijack a train?"
"Twi..."
"Princess Celestia is going to have a fit when she hears I've failed! I'll be fired! I'll be sent back to magical kindergarten!"
"TWILIGHT!" Spike shouted.
"What?" Twilight asked.
Spike pointed at the energy collection machine, which was now at 94%.
"I think your ranting gave off enough energy to fill your machine thingy," Spike said.
"I'm not ranting; I'm simply stating the facts," Twilight said. "Anyone with an ounce of sense would—wait, it's full now?"
"Yep!" Spike said. "We've got all the energy we need for your potion experiment thing!"
"Yay!" Twilight cheered.
The next day, Twilight Sparkle set about making her fabulous, magic-enhancing Mountain Dew. Don't ask me how she did it. I know even less about magic than Applejack does. All I know is that Twilight somehow managed to use her unicorn energy to power the magic-based potion.
"Unicorn hair...herbs from Zecora...a bucket of turnips..." Twilight said, checking off all the items on her list. "I think that's almost everything."
Spike stood on a footstool, so he could peer into the cauldron. It was filled with a sticky, dull, red liquid.
"It looks like melted candles," Spike commented.
"And...there," Twilight said, putting a thermometer into the mixture. "That's the last thing I need."
"Uh...why is there a thermometer?" Spike asked.
"To regulate the temperate, of course," Twilight said. "The potion has to simmer at around 90 degrees, for two hours. Otherwise, it'll be too thick for ponies to drink it."
"Huh," Spike said. "How are you going to heat it up? Put it in the oven?"
"I thought you could do it," Twilight said.
"What? Me?" Spike asked, surprised.
Twilight tried not to roll her eyes; she had thought this part of the potion-making was obvious. "Well, of course! You're the only one I know who can breathe flames!" she said.
"Yeah, but...two hours?" Spike asked.
"It's a tough job, but that's why you're my #1 assistant," Twilight said, ruffling the spikes on top of Spike's head in a loving way.
"Hmmph," Spike said, crossing his arms.
Monitoring the temperature of the potion was simple. Boring, but simple.
It all would have gone perfectly, if it wasn't for Pinkie Pie. The innocent little disaster had come into the library, in order to renew her copy of Non-Stop Fun: The Party Pony's Guide to Celebrating Just About Anything. As luck would have it, Pinkie Pie managed to appear during the twenty minutes when Twilight Sparkle was absent.
"Heyyyy!" the pink pony said. "Whatcha doin', Spike?"
"I'm keeping this potion warm for Twilight," Spike said, bored.
"Oooo, cool!" Pinkie Pie said, looking at the cauldron. "What's it do?"
"Supposedly, it makes your magic stronger or something like that," Spike said. He sighed deeply. "I think it'll be ready in an hour or so."
Aw, he sounds bored! Pinkie thought. I know! A joke will cheer him up!
"Hey, Spike!" Pinkie said. "What's big and hairy and has fourteen legs?"
"I dunno," Spike said. "What?"
"I don't know either, but it's standing right behind you!"
"AUGH!" Spike shouted. He literally jumped off of the footstool, then his leg caught on the cauldron rim. With a small splash, he fell face-first into the cauldron.
"Ha ha ha ha!" Pinkie laughed. "I'm just kidding! There's nothing behind you—Spike? Are you okay?"
"Blffffhfhf!" Spike said.
Pinkie grabbed Spike by the tail and pulled him out of the cauldron. He landed on the floor a short distance away. He stood up to glare at Pinkie Pie, as he wiped the potion off his face. "What's the big idea?" he asked. "What's wrong with you?"
Pinkie's lowered her head in shame. "It was just a joke..." she said sadly. As a general rule, Pinkie didn't like seeing her friends get mad. She also didn't like it when nopony laughed at her jokes. She lifted up her head to apologize to Spike, then stopped.
"Spi...Spi...SPIKE?" she asked, her pupils shrinking in fear.
"What?" Spike asked.
"You...you..." Pinkie said, lifting a shaking hoof at him.
"Huh? Ah!" Spike cried.
Changes were happening to the baby dragon. His stomach and tail shrank to nothing, while his neck stretched out. A shift in his gravity caused him to fall forward, on his...hooves? Spike looked at his claws in amazement, as the fingers slowly disappeared.
"What...what happened to me?" Spike cried. He tried to take two steps towards Pinkie Pie, but he slipped and fell flat on his face.
"Oh, wow!" Pinkie said. "I know what that potion does! It turns you into a unicorn! Cool!"
"Unicorn?" Spike asked. He raised a hoof to his forehead, and it bumped into something that wasn't there a minute ago.
"Mirror! Mirror! Mirror!" Spike shouted. He ran to the closest mirror, but he wasn't used to moving in his new body yet, so he tripped over himself twice. When Spike saw his reflection, he screamed. The purple unicorn inside the mirror screamed back at him.
"How exciting!" Pinkie Pie said. "I've got to try it!" She hopped to the cauldron and dunked her head inside.
"Pinkie, no!" Spike cried, but it was too late. When Pinkie brought her head back up, she had a brand new horn, sticking out of her head.
Spike slapped his face as hard as he could. This had to be a dream. It had to!
"Oh, yeah!" Pinkie said. She focused her energy on her horn, and it started glowing pink. "Say hello to Pinkie Pie, Equestria's newest unicorn!"
"This is a disaster," Spike moaned, slumping down on the floor.