I am He as You are She as You are Me and We are All Rule 63'd
Chapter 2: I am He and She is Me
Dusk and Twilight were returning to Ponyville. Twilight's Ponyville. Now that they had learned Spell 63, their respective teachers had decided that the purple unicorns should be the ones that introduced the residents Ponyville to their gender-reversed counterparts. They hadn't said why, but the raised the Sun... well, the Suns. Nopony cared why they wanted anything done, so long as it got done.
***
"Well, girls, that's basically it. Any questions?" asked Twilight, as the other Mane 6 (and one member of the Male 6) stared at her with half-glazed eyes.
"Uh, girls? Dusk? Wow, I actually just bored myself. I'm so proud of the me that bored the stallion-me. In fact, I think I'll squee."
At this, Pinkie dove into action, as nopony could squee over boredom. Not on the watch of Pinkamena Diane Pie III. NOPONY. She punched Twilight in the... what? I'm not allowed to make Pinkie hurt anything without going full-on Cupcakes? ("Cupcakes" here referring to the play written by her sister Inkie Pie, the famed Manetreal playwright, about Pinkie's foalhood idea that cupcakes might be able to feel pain) Drat. Okay, Pinkie decided to throw a "Welcome-To-Our-Universe-and-Good-Luck-With-Introducing-Everypony-To-Themselves" party. It kinda sucked. Anyhoof, the following day Twilight and Dusk decided that they begin their long, tedious task by introducing their respective #1 Assistants.
***
Spike was busy reshelving the Fiction Section, when he heard a call from the above floor.
"Spiiike! Could you come here, my little indentured servant?"
Twilight. Great. I have actual work to do this week, but does she care? No! I have some quality Rarity-slaving-for time scheduled today, and she knows that! "I'm coming, Twilight!" Now for the greatest enemy of all non-winged quadrupeds ... stairs.
When Spike had finished ascending the devil's creation, he saw Twilight and Dusk awaiting him. Wait, had Dusk been up there all night?
"Uh, Dusk, I don't see another bed, so... where'd you sleep last night?" asked the befuddled infant dragon.
"You uh, you don't want to know," said Dusk, whilst looking downward and blushing. "Anyhoof," he said, raising his head with a grin, "Let's get you two acquainted!"
As he said this both his and Twilight's horns began to glow, and a swirly blue vortex opened. Out of said vortex came a small, purple-and-green (female) baby dragoness. Already up-to-speed on the situation (everypony in Dusk's Ponyville was), Spines walked over to her doppleganger (it's all relative, baby).
"So... you're me?" asked Spines, "No offense, but I can't wait to meet the female Elusive."
"Elusive?"
"Oh, right. You don't know his name... but you definitely know hers."
Spike, realizing what she was getting at, gasped.
"Oh, you mean Rarity!" he exclaimed.
Seeing that this was getting awkward (and that they'd already completed their observations of this encounter), the lavender unicorns decided it best that they intervene in the conversation.
"Uh, Spines, Spike, we're going to need you two to write down our notes on the other ponies' interactions with themselves," Dusk said, "By the way, that was a strange sentence. I mean, I have, and will probably will still use(d) many stranger ones this week, and-- TWILIGHT, THAT'S NOT FUNNY!" Twilight stopped snoring, and laughed.
"Turnabout is fair play, my good self. Uh, wait, I should find some kind of common noun to refer to you as, so that I'm not constantly saying your name," pondered Twilight. "What do you think, Dusk?"
"Well, how about considering me some form of twin, as we are essentially twins (if you want to think about it in such terms)?" asked the studious stallion.
"OOH, I like that idea. Come along then, my metaphorical twin, let us screw with reality!"
As she completed her exclamatory sentence, she ran (uh, tumbled) down the stairs of the library, then into the street. Dusk facehoofed, Spike sighed, and Spines gasped, as they all went into the street to see if she was okay.