In her castle's study, Twilight was studying an ancient magical artefact. It was a small, edgeless stone, covered in strange markings. It had been uncovered during an archaeological dig in Southern Equestria, and sent to Twilight under Celestia's recommendation. Naturally, Twilight relished the opportunity to uncover the secrets of this unique object.
"Fascinating." She mused, examining the markings through a magnifying glass. "Almost like Coltic runes. But they're way too smooth." She levitated over some books on ancient artefacts, hoping to find a clue of some kind. "This may take a while..."
Twilight started to look through each of the books in turn, examining each page intently.
"Nothing in 'Ancient Artefacts Made Easy'." She frowned as she closed one book. "Maybe I should try 'Enchanted Carvings of Yesteryear'..."
As she opened the book, she found a miniature Discord inside.
"Or you could ask somepony who's actually been a stone before." Discord suggested.
"Ah!" Twilight dropped the book in shock.
"Careful!" Discord leapt out of the book, expanding to full size. "You'd think a well-known bookworm like yourself would be more careful with her reading material..."
"Not that I'm not happy to see you, Discord, but this really isn't the best time." Twilight declared. "I'm busy with a research project."
"Yawn." Discord grimaced. "Leave it to you to have the most boring way of passing time in Equestria."
"Celestia specifically requested my assistance." Twilight said proudly.
"Well, of course she did." Discord smirked. "The soon-to-be ex-ruler of Equestria's not wasting any time in unloading work onto her successor, is she?" He conjured up a bunch of scrolls (all of them having the word "work" written multiple times on them), which dropped onto Twilight, briefly burying her. "Then again, she always expected you to do everything for her. Does that make her a wise ruler, or you her unknowing patsy? Quite a conundrum, isn't it?"
"Celestia's been busy running a country for the last thousand years." Twilight pointed out as she emerged from the pile of scrolls. "You can't blame her for delegating some jobs to others."
"'Delegating'? Is that what it's called?" Discord countered. "I always thought the term was 'pass jobs I can't be bothered to do myself onto some adoring lackeys'. She probably wants to squeeze as much work out of you as possible, before finally giving up the throne. I have to give her credit for such low cunning, though..."
"...It's because you're bored, isn't it?" Twilight surmised cooly. "That's why you're annoying me."
"Don't flatter yourself." Discord scoffed. "There are ponies I can annoy with far less effort... And far more entertaining results." He snickered. "I just thought I'd drop by and say hello, like any good friend would."
"Well, you didn't actually say hello." Twilight shrugged. "But you definitely dropped by. So if that's all, I really must get back to work."
"And what exactly is this 'work' of yours, may I ask?" Discord asked haughtily. "Something to do with stones, right?"
"Just one." Twilight clarified, pointing out the stone on the table. "I'm trying to figure out exactly what it is, and what it does."
"Is that all?" Discord said dismissively. "Then why didn't you just ask Pinkie Pie's rock-crazy sister to take a look at it? Maddie, I think her name is..."
"It's Maud, actually." Twilight corrected him. "And I already asked her to take a look. She was able to tell me what kind of stone it is, how old it is, and a lot of other interesting tidbits. But nothing about what these markings could possibly mean."
"What markings?" Discord picked up the stone and examined it through a comically-large magnifying glass. "These markings?"
"Careful!" Twilight used her magic to pull the stone from Discord's grasp. "That stone is thousands of Moons old!"
"I'm just taking a look." Discord said indignantly.
Discord's eagle talon glowed yellow as he clenched it, and Twilight's magical aura was replaced by a similar glow. The stone flew back toward him.
"You can look, but don't touch." Twilight insisted, her own aura flowing over the stone again. "This is a piece of history. It doesn't need to become several pieces!"
"Are you calling me clumsy?" Discord scoffed, tugging the stone back magically. "I deeply resent that! Besides, it's not like its made of glass."
"I'd prefer not to take the risk." Twilight shot back, dragging the stone back her way.
"You didn't seem to mind Madeline getting her hooves all over it, did you?" Discord said petulantly, pulling the stone back.
"It's Maud." Twilight pointed out, returning the favor. "And she knows and respects rocks."
"Whatever." Discord scoffed, tugging back.
As they continued their magical tug-o-war, the markings on the stone began to glow; first the magenta of Twilight's magic, then Discord's yellow, and finally a bright white light that grew brighter by the second.
"What's going on?" Twilight frowned. "Discord, what are you-?"
"I'm not doing this." Discord insisted. "It's not me, honest!"
The white light erupted into a powerful glare that filled the entire room with blinding whiteness. Seconds later, it faded, as if it were never even there, and the stone dropped onto the floor.
"What was that?" Twilight groaned, her eyes still bleary from the flash of light.
"No clue." Discord's voice answered weakly. "I'm stumped. Which doesn't happen very often..."
As Twilight's vision cleared, she got the distinct feeling that everything in the room was smaller than it was a moment ago. Her table seemed further away, and her line of sight seemed level with the top shelf of the bookcase.
"What just hap-?" As she looked around more, she saw the strangest sight of all: herself, standing beside her (yet much lower), rubbing her eyes with a hoof. "Now this is really getting weird..."
But it was about to get weirder.
"What are you talking about?" Discord's voice emitted from the other Twilight's mouth. The other Twilight's eyes opened, revealing them to have the yellow sclera and mismatched red irises usually possessed by Discord, and the figure before Twilight stared up at her with abject horror. "No. Way."
Struck by a terrible thought, Twilight glanced into a nearby mirror, and saw Discord's face (with her own purple eyes) staring back at her.
"I... I'm you." She glanced back at Discord, a look of terror on her former face.
"And I'm you." Discord pointed a trembling hoof at his former body.
For a moment, the full scale of their situation sunk in. Then...
"ARRRRRGGGHH!!" They screamed in unison.
"You're me!" Twilight helped.
"You're me!" Discord yelped.
"ARRRRRGGGHH!!" They screamed again.
Just then, Spike burst into the room.
"Is everything okay in here?" He asked. "I thought I heard somepony screaming-"
"Spike!" Twilight declared. "We're in trouble!"
"So it's a good thing you're here." Discord snarked.
Spike stood in place, frozen with shock by the bizarre scene before. Then the corner of his mouth started twitching, which quickly gave way to a torrent of hysterical laughter.
"BWA-HA-HA-HAA!" He chortled loudly. "HA-HA-HA!"
"It's not funny!!" Twilight and Discord said in unison.
"You're right... It's hilarious!" Spike guffawed. "Ha-ha-ha!"
"You are not helping." Discord scowled.
"Remind you of anypony?" Twilight deadpanned.
After taking a moment to get his laughter under control, Spike appraised the situation.
"So... How did this happen?" He asked.
"Don't look at me." Discord said indignantly. "As if I would ever trade my handsome face for the lavender look..."
"If it wasn't you, then it must've been the stone." Twilight surmised.
"The stone?" Spike frowned. "The stone Celestia sent you?"
"It's the only viable explanation." Twilight declared. "It somehow caused us to switch bodies. If we can figure out exactly how it happened, maybe we can undo it."
"And how do you suggest we do that?" Discord asked.
"Only one way: research!" Twilight grinned.
"Oh, joy." Discord cringed. "Like this day wasn't already bad enough..."
"Wait, don't you have Discord's magic?" Spike asked Twilight. "Why don't you try to use it to change yourselves back?"
"Maybe I would... if I had the faintest idea how it works!" Twilight waved Discord's mismatched arms around. "Are you even able to switch minds?"
"Can't say I've ever tried." Discord shrugged. "I wouldn't recommend trying, in any case. Chaos magic can do almost anything, but in the hooves of an amateur -no offense- I'd actually prefer the research."
"Then we're agreed." Twilight nodded. "Spike, bring us all the books on ancient spells and artefacts we've got."
"Will do." Spike snapped a quick salute.
"In the meantime, let's work with what we have." Twilight stated. She glanced at Discord's mismatched paws, and attempted to make them snap. "Come on..." She growled. "How do you work these things?"
"Here, let me show you." Discord scoffed. "Anything to keep you from making my body look ridiculous..." He manipulated the digits into the right positions. "There. Now... move this claw downward."
Twilight complied, and heard the telltale snap. A nearby book disappeared off the shelf and appeared in the other claw.
"I did it!" Twilight cheered.
"Yes, yes, you get a gold star." Discord said sarcastically. "It's only one book, you know. I could easily do the same with your magic."
"Could you now?" Twilight countered.
"Yes, I could." Discord nodded. As he screwed up his face in concentration, Twilight's glowed, as did every book on the shelf. "Here they come!"
"Discord, maybe you shouldn't try so many at-!" Twilight started.
She was interrupted by all the books flying toward them at once.
"Ahh!" She ducked, waiting for the impact. But none came. She looked up, and saw the books hovering in mid-air totally stationary.
"Told ya." Discord bragged.
"Very funny." Twilight scowled.
"I thought so." Discord chuckled. "Now, shall we-" He started, turning away.
The magical aura suddenly faded, and the books all dropped to the floor.
"What was that about?" Discord frowned.
"You stopped focusing on the books." Twilight pointed out. "Pony magic requires the caster to concentrate on what they're using their magic on, not let it run wild. Let me show you how it's done."
"Oh, would you, please?" Discord said petulantly.
Twilight snapped Discord's talons, and, one by one, the books flew upwards and began to slowly form a stack.
"Very impressive." Discord snorted. "Think you can pick up the pace?"
"I'm trying." Twilight snapped again. "But I'm also trying to get them stacked in perfect alignment-"
"You're thinking too much!" Discord scoffed. "Chaos is spontaneous, spur of the moment, not carefully planned!"
"I can be spontaneous!" Twilight protested.
"Sure you can." Discord rolled his eyes. Activating Twilight's horn, he formed a stack of his own out of the other books, one that was very uneven. Moments later, Twilight had finished hers. "Now, can we finally get down to business?"
"Of course." Twilight opened the first book.
For the next hour, the duo pored through each book in turn, hoping to find something regarding the strange stone. While Twilight was in her element, Discord was struggling to maintain his focus.
"Ugh, so many pointless facts." He closed one book and reluctantly moved to another. "How does your brain not melt from boredom?"
"Maybe because I actually enjoy studying?" Twilight retorted. "When you can't solve most of your problems with a snap of your claws, it helps to actually know about things."
"It helps to be an egghead, you mean..." Discord muttered under his breath.
A blueberry pie suddenly landed on Discord, splattering all over his current head.
"What the-?!" He spluttered. Wiping the berry juice off his face, he saw Twilight smirking at him.
"I'm starting to see the appeal of this chaos magic of yours." Twilight chuckled.
"This is no time for inane pranking!" Discord snarled. "We need to focus, examine the problem from every angle, and- Wait. I sound like you."
"And childish pranks like that aren't my style." Twilight frowned. Another terrible thought came to her. "...What if there's more to this than just a mind swap? What if, slowly but surely, we're starting to take on each others' personality traits?"
"Are you serious?" Discord gaped. "You mean I'm going to end up as an upright bookworm for the rest of this body's depressingly small lifespan?"
"And I may end up as an all-powerful prankster for all eternity." Twilight cringed.
"Yes, because that would be so terrible." Discord snorted.
"Maybe not for you." Twilight admitted. "But that's not who I am."
"That's certainly true." Discord noted. "Plus, I doubt the citizens of Equestria would take kindly to their new leader's new look."
"Then we have to keep looking!" Twilight urged. "Who knows what'll happen if we leave this too long. Our bodies could be switched back, but the personality swap could be permanent!"
"Back to hitting the books, then." Discord nodded. "Never thought I'd say that. ...Or actually start to relish the prospect..."
The bodyswapped duo returned to their studies. While Discord started to slowly put more effort into his work, Twilight was finding it increasingly difficult to focus. Her attention started wavering. As Discord finished one book and moved to another, a devious smile lit up her face.
As Discord reached for the book, Twilight snapped her newfound claws, and the book flew into the air, flapping its pages like a bird.
"Too slow!" She taunted.
"Seriously?" Discord scowled, trying to ensnare the book in Twilight's magical aura. "Now?"
"Oh, lighten up!" Twilight cackled.
"I need that book, Twilight!" Discord snarled.
"You need a book? Then here you go!" Twilight grinned wickedly.
A large encyclopedia suddenly appeared in the air, dropping down on Discord's borrowed hooves.
"Yeow!" Discord yelped.
"Ha-ha-ha!" Twilight giggled.
"You do realise this is your hoof you just hurt?" Discord pointed out.
"Not right now, it isn't!" Twilight chuckled. "Come on, Mr. serious. Don't tell me you're lost your sense of humor already!"
"TWILIGHT!" Discord snarled.
Driven by anger, a blast of magic flew out of Twilight's horn and across the room, missing Twilight, but landing a glancing hit on the mirror, causing it to shatter. The sound snapped Twilight out of her revelry, and back to reality.
"I... I'm sorry, Discord." She apologized. "I just... lost myself for a moment there."
"Well try to hold on to your self for a little longer." Discord scowled. "We still need to find out how to fix this."
"And soon..." Twilight said, wary of what could happen the next time she lost control.
As Discord returned to his studies, he glanced at the encyclopedia that fallen on his hoof. His initial thought was to cast it aside. But as he looked at it, he found an idea forming in his head.
"Wait a second..." He mused.
For the next ten minutes, Discord searched frantically through some books. Then...
"I think I found it!" Discord yelped.
"You did?" Twilight moved over to look. "Where?"
"Here." Discord placed his borrowed hoof on the page. "A small footnote in the back of the Encyclopedia Obscurica led me to a section on magical artefacts from the pre-Celestial era in Epoch of Enchantment, and I think I've found what we're looking for!"
"Then let's hear it." Twilight urged, moving in for a closer look.
"According to this, one of the ancient Unicorn tribes created an enchanted stone that would allow those who held disputes with each other to switch places for a day, enabling them to see things from the others' point of view." Discord announced. "They called it 'The Switching Stone'."
"Wow, you found it. I'm impressed." Twilight smiled.
"Yeah, I'm just that good." Discord smirked.
"Guess being a bookworm isn't so bad, huh?" Twilight teased.
"Maybe..." Discord admitted. "But I wouldn't have thought of checking the Obscura in the first place if you hadn't dropped that regular encyclopedia on my- I mean, your hoof. So you have to admit being a prankster has its positives."
"I guess so." Twilight admitted. "Now, does it say how it works?"
"Apparently, we just have to funnel a little of our own magic into it at the same time." Discord read.
"That explains it." Twilight facepawed. "We must have triggered it accidentally when we were fighting over the stone."
"That sounds about right." Discord nodded. "But what I don't get is why our personalities are also being switched. There nothing about it happening in here."
"Maybe it's because the stone was meant for Unicorn magic." Twilight deduced. "My Alicorn magic and your chaos magic must have kicked the effect up a notch."
"Good thinking." Discord nodded. "Good to know the real Twilight is still in there."
"Thanks." Twilight smiled. She picked up the Switching stone with Discord's glowing eagle talon. "Shall we?"
"With pleasure." Discord grinned, lighting up Twilight's horn.
Their magical auras covered the stone, inducing another blinding white flash.
When the light faded, Twilight waited for her vision to clear again. She looked down, and to her delight, saw her own front hooves on the floor below her. She looked back up, and saw Discord's grinning face before her.
"Are you...?" She asked.
"Are you...?" Discord inquired.
"YES!!" They cheered, hugging each other tightly.
"Well, this was... An experience." Twilight admitted as they parted.
"So true." Discord agreed. "Some things are too weird even for the lord of chaos..."
"At least now we know what this stone can do." Twilight noted, as Discord handed the stone to her. "Celestia is going to find my report very interesting. And I think we learned a little more about each other, too. The stone got to fulfil its purpose one last time..."
"...Well, I should probably be going now." Discord said wearily. "Never let it be said I don't know when I've outstayed my welcome. Actually admitting it, on the other hoof, is much more rare, so enjoy this non-standard occurrence..."
"You don't have to go right away." Twilight spoke up. "We'll be having dinner in ten minutes, and you'd be more than welcome to join us."
"Really?" Discord smiled.
"Really." Twilight nodded. "Besides, you haven't lived until you've tried Spike's nachos."
"Well, I suppose I could stick around a little longer." Discord grinned. "And if you're in need of a good dessert, you know as well as I do that I make an excellent blueberry pie."
"I do now." Twilight chuckled. "But we've already got dessert covered. Red velvet cupcakes, fresh from Sugarcube Corner."
"Delish." Discord licked his lips. "But first, let me be a considerate guest and clean up."
One claw snap later, and all the books had returned to their proper places.
"Impressive." Twilight smiled. "If the 'lord of chaos' thing doesn't work out, you'd make a great librarian."
"No thanks." Discord snorted. I think I've had enough of books to last even my lifetime."
"As for me, I can never get enough of books." Twilight noted. "I guess at the end of the day, we're just two very different creatures."
"Not that it's a bad thing..." Discord smiled.
"Definitely not." Twilight agreed.
As they left the library, the Switching Stone gleamed in the afternoon light, almost as if it were beaming in pride at having brought another pair closer together.