*KNOCK–KNOCK*

The insistent nature of the knock, audible even all the way on the top level of the library, made Spike think that it wasn't the first knock at the door — just the first one that had managed to catch his attention. It didn't surprise him; he was admittedly distracted today, and who wouldn't be, if they had woken up to find their sister, mentor, and best friend transformed in such a fundamental way?

And then to make matters worse, there had been Twilight's mysterious disappearance from her bedroom. It wasn't like Twilight to head out without telling Spike that she was leaving — if only to make sure he was looking after the library — and it certainly wasn't like her to leave without actually going downstairs or opening any doors. Sure, if she was in a hurry, Twilight tended to start teleporting around everywhere rather than simply walk, but that wasn't exactly a possibility today, now was it?

Spike glanced at the clock as he headed downstairs, seeing that Twilight still had about forty minutes left. He knew how much having the Princess contacted about her problems worried her — though it was necessary sometimes — so he had resolved to hold off on sending Celestia a letter until a few hours had passed with no sign of her. Spike hadn't quite figured out what to do about the library in the meantime, however, and until he had heard the knock, it hadn't been important.

He made his decision as he reached the door: opening the library would involve having to explain where Twilight was, an explanation he didn't actually have, so he'd keep it closed. "Hello?" he called through the locked door, hoping his voice wasn't too muffled. "Due to, uh, some difficulties we're having, the library is closed for the day. We're sorry for the inconvenience."

"Spike, let me in!" came the exasperated reply, in a voice that made Spike's eyes widen.

"Pinkie?" he asked incredulously; she had been the last pony he'd expected to show up, but now that he thought about it, perhaps the party pony needed to talk with Twilight about her newfound powers.

Before he muster a longer response, the handle of the door was surrounded in a light blue glow, Spike's eyes widening as the lock turned all on its own. No sooner had the door unlocked with a faint click than it was violently thrown open, the sheer force of it knocking the young dragon head over heels into the bookshelves across the room. Shaking his head to clear his dizziness, Spike looked up from his position on the floor as a pink unicorn with straight hair and a determined look on her face strode into the library.

"I need books!"

"And so the transformation is complete," Spike muttered as he pulled himself off the ground, the motion of him pushing the fallen books off of himself drawing Pinkie's attention to him.

"Spike!" Determination was replaced with concern as she raced towards Spike, bending down to take a close look at him. "Oh my gosh are you alright I'm sorry I didn't mean to hurt you I'm so sorry I—"

"Relax, Pinkie, I'm fine," Spike said, forcing a small grin for the baker's benefit. "Thick scales, remember? Gotta say, though, if you're here to see Twilight, I've got some bad news..."

Pinkie shook her head. "Oh, I'm not here to see Twilight, I already saw her! No, I'm here for—"

"Wait, what?!" Spike interrupted for a second time. "You saw Twilight? When? Where?"

"Oh, she showed up at Sugarcube Corner just a little while ago!" As Pinkie spoke, her horn began glowing, and the books that had fallen from Spike's collision floated into the air. "She got stuck in the mirror, but I helped pull her out, and then we talked a bit about, um—" She glanced away for a second, suddenly very interested in the books she was reshelving with her borrowed magic. "—well, a few things. And then she decided she was going to throw me a party!"

Spike didn't know where to start. Did he want to know what Pinkie meant by "stuck in the mirror"? And what was it that she'd talked to Twilight about that she seemed very reluctant to mention now? The young dragon decided to skip those points and tackle the one at the end. "She's holding a party for you? Really?"

Pinkie chuckled nervously, sitting down to bring her forehooves together. "Eheh, yeah, I may have taken advantage of a tiny little weakness of hers in order to get out of an awkward conversation..." She closed her eyes and shook her head, smirking a little bit. "I didn't expect her to turn it into a party for me, though."

"Awkward conversation? Oh, come on, Twilight didn't choose today to tell you about— er, I mean—" Spike's mouth acted before he could think, and as Pinkie opened her eyes to give him an inquiring look, he knew he had just messed up.

"Tell me about what?" The perplexed pony stood up and walked up to Spike, not stopping until her snout was less than a hoof from his face. "Spike... do you know about Twilight's... feelings?"

Though the intensity of Pinkie's gaze was still making Spike a bit nervous, her question triggered a wave of relief through the dragon's body. He'd screwed up, big time, touching on a secret of Twilight's that not even the mare herself knew that he knew, but it seemed Pinkie knew about it already, so everything was alright. "Yeah. It's not like she told me anything, but... I've lived with her my whole life, y'know? Twilight's kinda an open book to me." Pinkie smiled at that sentiment, and that smile burned away the rest of Spike's nervousness. "So she did tell you about how she feels about you?"

"No, no, she showed me... although I'm pretty sure she didn't mean to." Finally shelving the last of the books in her magical grasp, the pink pony began to wander over to the card catalogue. "The spell she cast showed me her feelings — all of her feelings. I know that she likes me, I know how she feels about liking me, her nervousness about it, her doubt... Things I wouldn't have known about even if she'd come right up to me and asked me out on a date." She shook her head as her horn glowed once again, pulling open one of the drawers in the catalogue. "It's too much, too much! So I'm not dealing with it, not today, not when I have this opportunity!"

"Opportunity?" Spike asked as he walked over to Pinkie.

"In this very community!" Spike blinked at the odd response, giving Pinkie a chance to pull some cards out of the catalogue. Floating them in front of the baby dragon, she explained, "Magic, Spike! If I'm right in my party calculations — and I'm always right in my party calculations — Twilight will need approximately an hour and seventeen more minutes to finish acquiring what she needs for her totally super party. So I have just over an hour to learn all the magic I can!" She flashed a winning grin at Spike. "No problem when I have help from the librarian's number one assistant, right?"

Spike knew that his ego was being stroked, but he didn't mind. Grabbing the offered cards out of the air, he replied, "Sounds good to me! Where do you want to start?"

"Teleportation!"

When one's life is suddenly thrown for a loop, one takes extra comfort in that which hasn't changed, that which remains familiar.

So far today, Twilight Sparkle had awoken as an earth pony with her friend's cutie mark after a spell of her own casting, had gotten trapped in a strange and deserted alternate dimension for hours on end, had been forced to confront her friend about feelings she had long held but done nothing to act upon, and was now under the thrall of an irrepressible urge to assemble a mind-blowing party in a matter of mere hours.

To Twilight, the hastily-scrawled checklist on the ground before her was her best friend in the entire world right now.

"'Deliver Invitations,' check!" Twilight declared out loud as she pressed a check-shaped stamp against the corresponding square, leaving a black checkmark in its wake. "'Ignore Just How Fast You Managed to Deliver the Invitations—'" A strange twinge went through her face as she struggled to do just that. "—ugh, check. 'Purchase Checkmark Stamp so You Don't Have to Check Off Your List by Mouth,' check!" The former unicorn beamed at the three dark checkmarks she'd just stamped, before eyeing the twenty or so items still on her list. "I can do this, no problem! Pinkie won't know what hit her when she walks into the library. All I have to do is follow my list, and everything will be fine!"

Lifting up her hoof and letting the scroll return to its naturally rolled state, Twilight stuffed the checklist into one of her saddlebags as a steady drumbeat began to rattle off over the din of the busy Ponyville streets. She began to make her way to her next destination, her hoofbeats hitting the ground in time with the drums. Other ponies began to move out of her path, their instincts guiding them away from the mare in the spotlight. The drumbeat repeated over several measures as Twilight trotted down the street, gaining more and more complexity, until the eighth measure ended and Twilight finally joined her voice to the music.

"When I woke up this morning, my whole life turned upside down,

I was told to smile, but all I wanted to do was frown,

Now I am throwing a party, this urge I just can't resist,

But I'll get it done, I'll do it right, I'll check it off the list!"

Dozens of trumpets, trombones, saxophones, and clarinets blared their way into the rhythm as Twilight hit the final verse with gusto, picking up her pace and sliding through the door of Decor and Dishes, somehow acquiring a stylish purple fedora in the process. The drumline was reinforced by the deep tones of a double bass as the purple mare sauntered up to the counter.

"Hey there, how you doing, hear you got a sale,

I gotta make it quick, then I'm gonna bail,

I need streamers, confetti, whatever else I missed,

Give 'em to me quick and I'll check 'em off the list!"

Unfazed by the lyrical request, the shopkeeper floated packages of streamers, confetti, and a set of serving bowls into Twilight's waiting saddlebag, even as the singing mare fished some bits out of her other saddlebag and tossed them nonchalantly onto the counter. With a tip of her hat in thanks to the shopkeeper, Twilight danced her way out of Decor and Dishes, making her way across the street to a house that seemed to thrum with a beat unrelated to the current musical number. Rapping on the door in time with the tempo, the scholar only waited a moment before the door was opened by a pale unicorn, a pair of tinted shades propped up in her electric blue mane.

"Hello, Vinyl Scratch, Pinkie says you've got the beat,

My party needs DJ PON-3 to make it all complete,

I know it's short notice, but you're a true artist,

Here's my down payment, so I'll check you off the list!"

Vinyl chuckled in response to Twilight's stanza. "You're lucky I just happen to be free tonight. Sure, I'll play your gig." She grabbed hold of Twilight's offered bits with her magic and levitated the coins through her door. "Nice number, by the way. Kinda old-fashioned for my tastes, though it's got a swinging rhythm to it." She lowered her shades into place and flashed her new client a grin. "But tonight, I'll show you what a real beat is like."

Twilight responded with another tip of her fedora, the rhythm moving her hooves as she headed down the street once again. Her next destination was a few blocks away, and as she danced her way down Ponyville's main boulevard, ponies paused in their day-to-day routine to watch the latest musical number — and possibly join in should the choreography demand it. The brass section took up the slack left over by the lack of lyrics, a trumpet soloist providing colour to the rhythm as Twilight danced her way to her next stop.

The bell above the door was drowned out by the music in the air as Twilight waltzed — literally — into the sweet shop, setting her sights on the blue-and-pink-maned pony at the counter. The earth pony paused her conversation with a seafoam unicorn to look over at the new arrival, her eyes narrowing in annoyance. "Um, can I help you?" she asked, clearly not enthused by the prospect. In response, the music took on a darker tone, most of the brass instruments dropping out as Twilight began her next verse.

"Whoa, there, filly, I just want some tasty sweets,

I'm throwing a party for Pinkie, they're her favourite treats,

Without customers, your shop would cease to exist,

Don't cross me now, or I'll check you off the list!"

The fitting music made the words a lot more threatening than they would have been on their own, and Twilight quickly found herself loaded up with all sorts of licorice and jelly beans and hard candies. Leaving her bits — but no tip of her hat in thanks — the dancing mare quickly shuffled her way out of the shop. As the door closed behind her, she heard the unicorn turn to her friend and begin berating the earth pony. "Seriously, Bon-Bon, I love you, but you need to stop being such a—" The shutting door cut off the rest of the seafoam mare's comment.

Back on the street, Twilight's instincts told her that she needed to ramp up her number, but she dithered on just exactly how to — that is, until a familiar unicorn strutted by, her perfectly-curled mane practically shining in the sunlight. "Rarity!" she called out, rushing towards her friend as fast as her dancing hooves could take her.

"Why, hello, Twilight," Rarity began as she saw Twilight rushing towards her. "Would you happen to know who— wait, what are you— whoa-hoa-hoaaaaa!"

The fashionista's greeting turned into a surprised yelp as Twilight caught up with her and immediately swept her up into her hooves. Twilight lifted both Rarity and herself onto their hind legs, spinning her impromptu dance partner around before dipping her low to the ground. "Rarity, my dear—"

"Wait!" Rarity's command silenced Twilight's lyrics, the music dying down to a rhythmic beat as the unicorn righted herself and freed herself from her friend's hooves. Raising a hoof, Rarity said, "Just one moment," before quickly rushing off. Twilight was left blinking in confusion at what had just happened, frowning as she took out a brass watch and glanced at it. No more than ten seconds had passed before Rarity suddenly reappeared, now clad in a stunning white dress that sparkled in the afternoon sun, no doubt due to the tiny diamonds that covered the otherwise rather simple outfit. Approaching Twilight, the unicorn took her hoof and flashed her an amused smile. "Continue, darling."

Twilight offered a grin of her own as she used the leverage Rarity had given her to lift her friend to her back hooves again. "Rarity, my dear, I'm so glad you came along," she sang, the brass making its triumphant return to the song as she spun her friend over her back, leading Rarity towards the town hall. "I need a big dance scene to complete this song!" The two mares came apart as they danced their way up the steps of Ponyville's tallest building, where the band that had been playing all along was assembled on both sides of the wide front porch, mares and stallions alike wearing matching black suits and fedoras as they gave Twilight and Rarity something to dance to. "Let's show Ponyville something that shouldn't be missed!" Coming together again, Rarity turned the tables on her dance partner by spinning her around, bringing her in close as Twilight finished her stanza with, "Then I can go ahead and check this song off my list!"

The two came apart again to start dancing separately, Rarity employing some moves that Twilight easily matched with grace and style that the bookworm normally didn't possess. "Check one, check two, check three-four-five!" The two friends spun around each other hoof-in-hoof as they switched places up on the impromptu stage. "Checking off lists makes me feel alive!" Sliding across the porch, Twilight again put Rarity into a dip, before lifting her clear off of the ground and spinning around with Rarity in her forelegs. The band picked it up yet another notch as Twilight set Rarity down back on the ground and stepped forward.

"Tonight I'm throwing a party you won't want to miss,

And all of it an effort to earn that pink mare's kiss,

If I win her heart, I will know true happiness,

And then you can check! Me! Off! The List!"

Twilight accompanied her final words with a toss of her fedora into the crowd that had gathered before the town hall. The band followed her up with a rousing finale of their own, every piece of brass blaring at once before the drums that started it all brought it to a close.

And just like that, the song was over. The impromptu audience in front of the town hall quickly dispersed as the spectacle faded, the band following after them as the ponies returned to their day to day lives. A few of the musicians complimented Rarity on her dress as they packed up their instruments, the fashionista almost absentmindedly acknowledging their praise as her attention was focused on her purple friend. "Twilight, dear, that was— why, yes, sir, I did design it myself— Twilight, why— oh, no, I'm flattered, but I have prior plans tonight— I really must know—"

The last interruption was from Twilight herself, the purple mare raising a hoof as though to say "just one second" as she dug through her saddlebags and pulled out her list. Laying it down on the wooden porch and rolling it out, Twilight uncapped the checkmark stamp still wrapped around her hoof and glanced over the list. "'Purchase Decorations,' 'Obtain Services of DJ PON-3,' 'Acquire Sweet Snacks,' and 'Sing Jazz Orchestral Number About My Love of Lists,' all check!" Rolling up the scroll and placing it back in her saddlebags, Twilight turned to her friend. "Yes, Rarity, I'm an earth pony today. I cast a spell last night that switched things around with—"

"Pinkie, yes, dear, I figured as much." Finding that her interruption only earned her a raised eyebrow on Twilight's part, Rarity elaborated, "The rumours have been flying around town all morning, darling, how Pinkie has somehow grown a horn overnight and is now showing off her newfound talents at Sugarcube Corner. I was just on my there now to ascertain just how much truth there was to the rumours, but I suppose seeing you like this has made that a moot point." The unicorn trotted around her friend slowly, taking note of Twilight's transformed cutie mark as she did. "I'd ask you what possibly possessed you to cast such a spell, but I think I have a good idea after that number you just sang," she continued, a sly smile crossing her snout. "You were obviously motivated by 'that pink mare's kiss.'"

"Rarity!" Twilight's cheeks burned crimson at her friend's remark, a combination of embarrassment and shock that Rarity would say such a thing. "You are the last pony I'd ever expect to be that rude! I was singing! You're not supposed to bring up what I sang about!"

Having finished her circuit around Twilight, Rarity fixed her friend with a look that would have withered plants. "I never! Of all the things to accuse me of! I did not learn about your infatuation with Pinkie Pie from your musical number!" The primadonna looked away quickly, nose held high in the air. "I already knew."

"What." It wasn't a question. It wasn't even a statement. It was simply all that managed to come out of Twilight's mouth.

Rarity turned her gaze back to Twilight, offering her friend a generous and somewhat amused smile. "My dear, you aren't exactly the best at hiding your feelings. They've been an open book these past couple of months for anypony with even an ounce of romance in their hearts." The unicorn shook her head ruefully. "Which of course means only Fluttershy and myself have noticed. I had hoped you would eventually come to me for help, but—"

A perplexed expression had overtaken Twilight's features as Rarity had explained, until she finally had to interrupt her. "Wait, Rarity, what about Pinkie herself? I mean, I'm not the best judge of this, but I would say that Pinkie's a bit romantic herself... right?" She silently cursed how unsure she sounded; why couldn't these sorts of things be as easy to read as Ancient Equestrian?

"Ahh, well, I can only speak for what I believe, but Pinkie is very good at seeing and understanding other's feelings, with one terrible flaw: she can't figure out what other ponies feel about her in the slightest." Rarity gave a sad shake of her head, glancing down the street at the still-bustling bakery. "You saw it when we tried to throw her a surprise party, but that wasn't the first time it caused... issues."

Twilight nodded sagely, following Rarity's gaze for second before turning back to the unicorn. "Yeah, she totally misread the situation with Cranky as well."

Rarity seemed to hesitate a moment before continuing. "I'll confess, darling, that before you graced us all with your presence, we weren't all quite as close of friends with Pinkie as we are now. In fact, I'd say we were more... acquaintances. But I'm not certain Pinkie ever understood that. She tries to befriend everypony, as you well know, but she specifically latched onto a few, myself included, and gave us extra attention. And I... I resented her for it."

Placing a comforting hoof on Rarity's shoulder as she reminisced, Twilight offered a kind smile of her own. "Hey, I've been there. Remember how I spent most of that first party she held for me? Locked in my room, trying to ignore it." Rarity chuckled at the memory as Twilight continued, "Pinkie's affection is an acquired taste, to be certain, but once you really let her in..."

"Agreed, darling, agreed," Rarity replied with a nod. "I only regret now having not let her in earlier. How much different things would have been when I was just getting started in Ponyville!" With a smirk, she glanced slyly over towards her friend. "But enough dwelling on the past! We should be concerning ourselves with the future, a future where you hope to acquire a taste of Pinkie yourself..."

"Rarity!" Twilight yelled once again, her blush returning with even greater intensity.

"Now, about this party tonight," Rarity continued as though she hadn't just scandalized Twilight, "I shall attend, of course — you did send me an invitation, correct? — and I shall help you navigate those treacherous waters to Pinkie's heart."

"Rarity, really, you don't have to—"

"No, no, darling, I insist!" The fashionista glanced up at the sun, frowning at just how much Celestia's charge had moved across the sky. "Oh, and time is running short. There's so much to do, a dress to make, lines to practice, and so little time!"

"Whoa!" Twilight cried out in surprise as Rarity's magic suddenly lifted her off the ground, her trained instinct to immediately counter such an invasion of space doing her little good as she found herself suspended off the ground.

"Come now, Twilight! We're going to make you a star!"

She was going to fall.

No, she wasn't. Pinkie had to reassure herself for the tenth time in the last minute that she was not going to fall through the clouds and become a smear on the road running underneath Rainbow Dash's cloudhome. She had read and reread the spell a dozen times, she had performed it easily, and it didn't matter because she had obviously miscast it so it would only last three minutes instead of three days and Dashie would wake up to find her broken and battered body below—

No! Not falling!

Why was it that when Twilight had cast this very same spell on Pinkie, she had jumped out of a balloon onto the cloudy surface of Cloudsdale without a second thought? Sure, Twilight was a whiz with magic, but they'd traded cutie marks! Pinkie should have all of the purple pony's prodigious power at her disposal! And yet Pinkie couldn't stop worrying that she'd messed up the spell somehow, screwed up in some indeterminable way.

At least she had found that slow fall spell in case anything did go wrong. Pinkie was certain that she could properly cast magic that she had found in a children's book titled My First Cantrips.

...almost certain.

Kinda certain.

Desperate to stop thinking about the terribly long distance to the ground, Pinkie distracted herself by looking around at Rainbow Dash's frankly amazing house. Logically (and that part of her really was being louder today, it wasn't just her imagination), she realized that a library built into a tree, a boutique built to look like a carousel, or even a bakery that looked like a gingerbread house were all pretty spectacular places to live. At this point, however, she'd been to them so many times — Celestia, she even lived in one of them — that she had grown accustomed to them; perhaps she even took them for granted.

But Dash’s home was something entirely new and exciting, somewhere she had never been. So despite the nagging fear that she was going to fall at any moment, Pinkie took her time to explore every nook and cranny she could find as she tried to find the pegasus’ bedroom. She splashed her hooves through the numerous rainbow waterfalls that flowed from the ceiling (but was careful not to actually taste any). She marvelled at the ridiculous kitchen with pantries extending higher than she could reach even if she created a magical clone of herself and stood on her own shoulders (and she could, now, thanks to her reading). She said hello to Tank, who had his own room with a whole floor made of stepstone; Pinkie had learned about the magical stone, only found on those few mountain peaks that touched the clouds, on her trip to Cloudsdale, and she knew enough to realize that flooring an entire room with the stuff must have cost Dashie a fortune.

Eventually, Pinkie found Rainbow Dash’s bedroom, with the pegasus in question sleeping away the afternoon in the comfort of her own bed, an open copy of Daring Do and the Feather of Fate cradled lovingly in her arms. The pink intruder took a moment to appreciate the sheer cuteness before her, and then she cast her eyes around the room, looking for the best tool to complete the task. This turned out to be one of Dash’s own feathers, moulted in her sleep, and now picked up with the lightest touch of magic. Pinkie brought the feather over to Dash’s throat, brushing it gently against her coat. “Wakey, wakey, Dashie~”

Rainbow Dash let out a giggle as the ticklish sensation invaded her dreams, before muttering, “C’mon, Fluttershy, knock it out...” To say Pinkie was intrigued by this reaction would be an understatement, but there would be time for delving into Dash’s deepest desires another time. The pink unicorn redoubled her assault with the feather, and this time, the sensation was too much for Dash’s mind to deal with without waking up.

The pegasus shot up in bed, blearily blinking sleep from her eyes. “Huh-wuh? Huh?” Dash managed to focus on the pink blob at the foot of her bed after a few moments. “Pinkie Pie? Why—” She interrupted herself with a big yawn. “—why did you— wait.” Dash’s eyes widened dramatically, her pupils narrowing as realization after realization hit her. “Why are you in my room? How are you in my room?! Why are you a unicorn? Oh, dear Celestia, why is your hair straight?!”

“Well...” Pinkie sat back on her tail in order to tap one of her hooves with the other. “I’m in your room because I need your help for a totally awesome prank that I can only do today.” She tapped her hoof in a slightly different place than before. “I cast the cloudwalking spell on myself — which seems to be working alright so far — and teleported up here.” Another tap in another position. “Twilight cast a spell last night that traded our abilities for the day.” And Pinkie finished with a final tap on the side of her hoof. “And I’m not sure, but I think my hair is straight because of the spell. Can’t be a hundred percent on that, though.”

To her credit, Rainbow Dash managed to not blurt out any objections to Pinkie’s answers, and as Pinkie finished her last point, a look of relief washed over the pegasus’ face. She continued to stare at Pinkie for a few seconds, making the pink pony increasingly nervous, before she closed her eyes for a second, shaking her head slowly as she softly muttered, “Pinkie Pie, you are so random...” When she opened her eyes again, they were filled with nothing but enthusiasm. “So... a magic-fueled prank, huh? What do you have in mind?”

With a squee of delight at Rainbow Dash’s interest, Pinkie Pie jumped onto the pegasus’ bed, her weight jostling her friend around. “Dashie, we’re going to stage the best prank in Ponyville history!”