Three Days Earlier
In the stallion universe, Dusk Shine was performing a magical experiment, with the help of his number one assistant, Spines the baby dragon.
"Just think of it, Spines," Dusk Shine was saying. "If this works, we'll be able to communicate with somepony from another dimension!"
"I understand that," Spines said. "I just don't understand why I have to play mailmare with them."
As usual, Spines was in charge of sending Dusk Shine's letters. Dusk didn't trust the ponies in town who delivered mail. The cross-eyed pegasus who covered most of town had a bad habit of crashing into things, and the mailmare who delivered mail on the edge of town tended to deliver bills to the wrong address, due to her bad eyesight.
"It'd be too dangerous for one of us to go through the wormhole," Dusk Shine said. "But sending a scroll? Piece of cake. Now let's get started."
Dusk began to read from the book on the ground in front of him. Concentrating with some difficulty, he managed to open an inter-dimensional wormhole, right in the middle of the library ceiling.
"Woah!" Spines said, jumping backwards in fright.
"You have letter ready?" Dusk asked.
"You bet," Spines said. She held up the scroll that Dusk Shine had prepared. "So, I just throw this in the hole?"
"No," Dusk said. "It's safest if nothing physically travels through the wormhole. Just send it like a normal letter, and I'll cast a switching spell on it."
"Okay..." Spines said. She took a deep breath, then blew green flames on the letter, transforming it into green smoke. The smoke wafted up towards the ceiling, where the wormhole was. Dusk Shine threw a switching spell towards the green smoke, completely unaware that Twilight Sparkle's summoning spell had slipped in, through the other side of the wormhole.
To explain it in non-magical terms: things went crazy.
"Is it supposed to do that?" Spines asked, as green mist seemed to cover the entire ceiling.
"I hope so!" Dusk said, suddenly fearing that monsters from another universe would attack.
The green mist turned brighter, then dimmer, and it condensed into a shape around the size of your average stallion, before it flew through the wormhole and disappeared.
Dusk Shine and Spines let out a sigh of relief. The ceiling of the library looked normal once again, if you didn't count the large wormhole.
"Great, I think they received the letter!" Dusk Shine said. "Next time, I should probably practice before trying to cast spells on mist."
"You BWAAAAARP!" Spines said, burping out a letter in the middle of her sentence.
"Yes!" Dusk Shine cried. He immediately closed the wormhole—which was taking way too much magic power to maintain, anyway—and walked over. "The letter from the other dimension! What does it say?"
"I can't believe they answered so quickly," Spines commented. She picked up the crumpled-up piece of paper and read it aloud.
Dear Princess Celestia,
Today, I learned that not everypony likes it when I sing in public. While singing can be an excellent way of relieving tension and showing your emotions, other ponies feel compelled to sing backup and dance along, whenever I start a song. This can put unnecessary pressure on them, especially the ones who aren't good at dancing to begin with.
Spike here. Personally, I think impromptu musical numbers are kind of silly, but I'd like to add that sometimes, I feel left out. I mean, Twilight and her friends sing all the time, but they almost never let me sing along with them.
Octavia was really nice when she helped explain this to me. You'd think she would be mad or at least annoyed. I know I would be, if I had to talk about the same thing over and over again, all day long, to a bunch of different ponies. But Octavia was still kind and helpful, as if I was the first pony who asked that day, not the four hundredth. I wish I could be as patient as her.
And the only time they let me sing, I have to sing backup. I think I should have a solo! Or better yet, I could start a band with Pinkie and the Cutie Mark Crusaders! We could call ourselves "The Dragon Explosion!"
Spike, are you adding your own commentary to my letters again?
Spike! Great, now I have to throw this letter out and start over from the beginning again!
[After this was a bunch of furious scribbles at the bottom of the page]
Dusk and Spines looked at each other.
"That's the letter they sent?" Spines asked finally.
"Heh heh," Dusk said, running a hoof through his hair. "I guess the closest letter the spell could find was inside a trashcan."
"Well, that certainly wasn't worth the effort," Spines said.
"Hey, it wasn't a total loss!" Dusk said. "We learned that the Spines in the other universe is called Spike...and she wants to start a band!"
"Not a bad idea, come to think of it," Spines said. "Maybe I should try to learn guitar!"
"Not as long as you're living here, you're not!" Dusk Shine said. "Those things are too noisy for a library!"
Dusk and Spines squabbled for a bit, the letter from another dimension forgotten. As it turned out, Twilight Sparkle never found the letter that Dusk wrote to her, mainly because it appeared inside her trashcan.
Shortly before Dusk's magical misadventure, back in the mare universe, Rainbow Dash was preparing something wonderful.
"This is gonna be awesome," Rainbow Dash said to herself, as she stretched her wings out in preparation for her latest stunt. "If the Wonderbolts don't accept me after this, then they're crazy."
Rainbow Dash's plan to impress the Wonderbolts dealt with her weather item of choice: rainbows. In her experience, rainbows generally tended to last for a minute or so, after it stopped raining in an area.
Being a pegasus pony, Rainbow Dash was able to grab a raincloud and set it off, near the edge of Applejack's farm. Rainbow was currently on the other end of the farm, using a pair of binoculars to examine the raincloud from a distance. Right on schedule, the cloud stopped raining, and a rainbow appeared.
"GO!" Rainbow Dash shouted, pumping her wings to the maximum.
The plan was simple. The rainbow from the rain cloud would stay in place, for about a minute. That was more than enough time. All Dash had to do was gauge the distance properly, and if everything went perfectly, she would perform a Sonic Rainboom from inside a rainbow.
Rainbow Dash wasn't sure what this would look like. Would it be a Double Sonic Rainboom? Would the Rainboom push the rainbow out? Would it have no real effect on anything, besides looking totally cool?
Rainbow Dash felt herself going up against the sound barrier, but instead of breaking through it, she maintained her current speed. Not yet...not yet...almost there...NOW!
A half-second before Rainbow Dash pierced the sonic barrier, Dusk Shine's inter-dimensional switching spell, combined with Twilight Sparkle's summoning spell, was set loose. Without knowing what was happening, Rainbow Dash winked out of existence in her own Ponyville, and she was transported to the stallion universe.
Where she immediately crashed into a tree. Unexpected inter-dimensional travel at high speeds can do that to you.
"Ow! What the hay?" Rainbow asked, getting back up to her hooves. "Where'd that tree come from?"
Rainbow Dash looked around, and it took a second to recognize this area.
"Hey, this isn't Sweet Apple Acres!" Rainbow Dash said. "This is near Fluttershy's! What gives?"
Rainbow Dash flew up and looked around. She couldn't understand it. Not only did she mess up her stunt, but she was nowhere near where she should be. If she didn't know any better, she'd say that she disappeared from one place and reappeared somewhere else.
"Maybe...maybe the stunt did work, and I just traveled super-far without knowing it?" Rainbow Dash wondered. She considered the possibility for a moment, but she dismissed it as impossible because there were no rainbows in the sky anywhere.
A little weirded out by the whole ordeal, Rainbow Dash decided to pick up her binoculars at Sweet Apple Acres, before going home and trying to figure out what went wrong. Either that, or she would go to sleep.
As she passed by Fluttershy's, Rainbow Dash saw her yellow friend out in her front yard, feeding some cats. Rainbow stopped suddenly, when she caught sight of her friend's short mane.
"Whoa ho ho!" Rainbow Dash said, laughing at the sight. "And people say I'm the tomboy!"
Rainbow Dash flew down to the ground. "Hey, Fluttershy, nice manecut!" she teased. "Your mane is so short, you look like—"
The yellow pegasus turned around and looked at Rainbow Dash. Fear covered every inch of his face, and Rainbow Dash was momentarily stunned speechless. Whoever this stallion was, he was not Fluttershy.
"—like a colt?" Rainbow Dash finished.
"I...I..." the yellow pegasus said. His eyes dashed left and right, and then he himself dashed—right inside the cottage, slamming the door behind him.
"What the hay is going on today?" Rainbow Dash wondered. Shaking her head, she flew in through one of the windows to Fluttershy's cottage.
"Eek!" the yellow colt screamed.
"All right, punk!" Dash yelled. "Who are you, and what are you doing in Fluttershy's house?"
"I'm...I'm Butterscotch," the yellow pegasus said.
"I didn't ask what color you are; I asked for your name," Rainbow Dash said.
"B-Butterscotch is my name," Butterscotch said.
"You were named after a candy?" Rainbow Dash asked. "That's kind of...well, whatever. You know you shouldn't be here, right?"
"I...I shouldn't?" Butterscotch asked.
"No!" Rainbow Dash said. When she saw the stallion flinch, she decided to ease up on her interrogation. The poor stallion was clearly scared out of his mind.
"You shouldn't break into other ponies' houses," Rainbow said. "I admit, you kind of look like Fluttershy—which is totally weird—but if she's not here, you shouldn't be here. Got it?"
"Eek!" Butterscotch said. "G-got it! Just please don't hurt me!"
"Relax, I'm not going to hurt you," Rainbow Dash said. "I'm just trying to help out my friend Fluttershy, is all. No big deal."
"I...I don't know who that is..." Butterscotch said.
"You don't know Fluttershy?" Rainbow Dash asked. Butterscotch flinched when she said this.
"I...I don't know a lot of ponies...especially mares..." Butterscotch said. "Mares are scary..."
Jeez, he should know Fluttershy, Rainbow Dash thought. He's the only pony I've met who's as shy as she is!
"Fluttershy lives here," Rainbow Dash said. "Which means you're trespassing on her property!"
"I...I own this cottage," Butterscotch mumbled inaudibly.
"What was that?" Rainbow Dash asked.
"I'm sorry, I'll never trespass again!" Butterscotch said.
"That's good," Rainbow Dash said. "Now let's go outside."
"Uh...uh...go outside with you?" Butterscotch asked. "No...I can't...what if somepony sees us together?"
Rainbow Dash sighed. This stallion was just as bad as Fluttershy, during one of her panic attacks. "Dude, just calm down," Rainbow Dash said. "You know, you've never going to get a marefriend with that attitude, Mr. Nervous."
Butterscotch trembled. Rainbow Dash had unknowingly hit upon a sore spot with him. During flight school, the other pegasi had teased Butterscotch about him and mares. They even had an impolite sing-song chant about it.
Rainbow stared at Butterscotch. "Uh...you okay?" she asked.
Then the dam burst.
"Waaaaaaaah!" Butterscotch cried, tears flying everywhere. "You're right! You're right! I'm never going to get a marefriend!"
"Whoa!" Rainbow Dash said, stepping backwards. She wasn't used to crying colts, and she definitely wasn't expecting Butterscotch to scream all of a sudden.
"Waaaaaah!" Butterscotch said, grabbing onto Dash's forelegs. "All...alone...FOREVER!"
"Hey, get off!" Rainbow Dash said, trying to remove her legs from the yellow pony's iron grip.
"Nopony will ever love me!" Butterscotch moaned. "They all avoid me, and I avoid them!"
"Look, I...I can help you!" Rainbow Dash said. "I'll get you a date! A marefriend! Anything! Just stop crying!"
The blubbering slowly stopped. "You'd do that for me?" Butterscotch asked.
"Sure!" Rainbow Dash said. "Just...never cry again, okay? I can't handle that kind of stuff."
"You...you're lying!" Butterscotch said. "No one can help meeeeeeee!"
"I know lots of mares," Rainbow Dash said. "I'm sure one of them would jump at the chance to date, uh, a hot stallion like you."
Rainbow Dash doubted this. As far as she knew, none of her friends had "timid" or "cries a lot" on the list of desirable traits for their dream stallions. Still, Rainbow Dash knew she could get a friend to go on at least one date with this guy. Pinkie Pie owed Rainbow Dash a favor, and Twilight Sparkle...
"Yeah, Twilight!" Rainbow Dash said. "She'd be perfect for you! She's not always good at dealing with other ponies, either!"
Tricking Twilight into dating this guy will be a snap! Rainbow Dash thought. All I have to do is tell her that it's a new kind of friendship for her to investigate. She'd eat that right up!
On second thought, Rainbow Dash considered, maybe she didn't have to trick Twilight into dating somepony. She didn't seem like the type of mare who had ever gone on a date. As in, ever. Twilight would probably jump at this opportunity.
"Who's Twilight?" Butterscotch asked.
"She lives at the library in town," Rainbow Dash said.
"She? You mean, Spines?" Butterscotch asked, confused.
"Spines? What the hay are you talking about?" Rainbow Dash asked.
"There aren't any mares in the library," Butterscotch said. "Dusk Shine lives there, with his baby dragon. Dusk is one of my best friends, along with Elusive and Berry Bubble and Applejack and—"
Rainbow Dash had no idea what Butterscotch was talking about, and once she heard a familiar name, she jumped on it. "You know Applejack, huh?" Rainbow Dash asked.
"But you don't know who Fluttershy is," Rainbow Dash said.
Butterscotch shook his head.
Rainbow sighed. "How could you know Applejack, without knowing me or Fluttershy? That's just weird," she said. "Okay, whatever. Just don't trespass anymore, you got that?"
Rainbow Dash didn't notice anything different as she flew through the town. There were more stallions than normal, checking her out. One or two even whistled at her, but she ignored them all because they were Earth ponies, and to be honest, Dash wasn't interested in Earth ponies.
That's not to say Rainbow Dash was discriminatory, or something like that. She just couldn't picture herself dating anypony who wasn't a pegasus; flying meant too much to her for that to work. And so she ignored the stares of the Earth pony stallions, as she flew to the library.
Rainbow flew in through the window, like usual. "Hey, Twilight, I found somepony who—" Rainbow Dash started, then stopped. The lavender pony in the library was not Twilight Sparkle.
The stallion turned around to greet Rainbow Dash, and his eyes widened. "Ruh—Rainbow Blitz?"
Rainbow Dash slammed her hooves against the ground. "All right, what's going on here?!" she demanded. "Where's Twilight Sparkle?"
Ten minutes later, the front door to the library slammed open, and in walked Elusive, the white-colored stallion who ran the Carousel Boutique.
"I got your letter and came right away," Elusive announced. "What's the emergency?"
"It's Rainbow Blitz," Dusk Shine said. "He's been turned into a mare."
"WHAT?" Elusive asked.
Dusk gestured to the corner of the library, where Rainbow Dash was. She waved a hoof at them. "Hey," Rainbow Dash said. "You must be the colt Rarity, right?"