Spike paced around the polished surface of the Cutie Map, brows furrowed and claws held nervously behind his back. Twilight had been gone for hours; far longer than they said they would be.
He didn't know the details; only that Twilight woke him up at the crack of dawn in a panic, practically dragging him out of bed to the Cutie Map room. When he asked why, Twilight only babbled something about not screwing up the timeline more than she already did, and her last words to Spike before she stepped through the time portal they had summoned above the Cutie Map was if they weren't back in an hour, assume the worst.
It had been four. Twilight's other friends sat at their respective thrones at the base of the map, watching Spike walk back and forth.
"What was so important that she couldn't bring any of us along?" Rarity asked, breaking the silence.
"Maybe she didn't have time?" Fluttershy suggested.
"That doesn't make sense. She could just go back in time and bring us back here so we could go back in time and..."
Rarity wobbled a bit. "Ugh. No wonder Twilight doesn't like messing with time magic."
"Look," Applejack interjected flatly, "Obviously Twilight couldn't bring us along as we'd be unaccountable chronomatic variables that would exponentially increase undesired fourth-dimensional outcomes in respect to the base timeline."
The others stared at her, sparking a scoff from the farmer. "What? Apple season ain't for another two months. I've been reading Twilight's fancy science books to kill time."
Rarity pointed to the shimmering distortion of light above them, the lingering signs of Twilight ripping a hole in spacetime. "Even if you're right, I feel rather helpless just standing around like this. Surely there's something we can do to help?"
They all turned to Pinkie, currently trying to balance a pyramid of spoons on her nose. She looked up, reading the expectations of her friends.
"Lemme guess," she began, "you want me to throw a 'Congratulations You Didn't Destroy Time' party?"
"Well..."
The pink earth pony hopped up in a huff, scattering the spoons everywhere. "Maybe I want a day to myself for introspection! And consideration! And maybe just a bit of meditative calm. Just every once in a while! To clear my mane, and recoup my energy. I'm not a bottomless void of hilarity, you know. This takes work!"
After an awkward silence, she giggled. "Just kidding. The marching band's outside."
Rarity sighed. "I was thinking more—"
Her sentence was interrupted by a bright flash in the middle of the room. The light above them seemed to bend inwards on itself, warping into pure possibility as it curved into a tunnel, throwing a very exhausted Twilight Sparkle onto the top of the map.
"Twilight!" Rarity cried, jumping up onto the table and running over to Twilight. The others followed, crowding around her.
Twilight pushed them away, weakly rising to her hooves. Just as she was level, she suddenly stumbled, prompting her to place a hoof on her head.
"Ugh..." she groaned. "Did it work?"
She shook her head, running over to Pinkie and grabbing her face, bringing it level to hers.
"Pinkie! When is the first time we met?" Twilight demanded.
Pinkie arched a brow, searching her memories. "Gotta consult the old archives for this one. It was...when you first came to Ponyville? Right before all that Nightmare Moon stuff happened?"
Twilight's expression softened, and she lot go of Pinkie's face with a relieved sigh. "Thank goodness," she breathed. "Looks like I've restored the timeline."
She turned to the rest of her friends, and suddenly her eyes went wide as she darted her head around the room in a frantic search. "Wait! Where's Glimmer?!"
Her friends cocked their heads, asking "Glimmer?" in unison.
"Starlight Glimmer!" Twilight elaborated. Pink unicorn? Unimaginably powerful magic? Tried to erase our friendship with time magic?"
Dash shrugged. "Yeah, doesn't ring a bell. Are you talking about that Time Dragon we fought once?"
Twilight recoiled. "Time Dragon? We never fought a Time Dragon!"
Spike pulled at Twilight's leg. "What are you talking about? It happened last month. We had to journey to the other side of the world, I got captured, it turned out the Time Dragon was my actually myself from an alternate future from the past..."
Pinkie's chest puffed out with pride. "I rode a moose!"
"Pinkie rose a moose..."
Twilight sat down, clutching her head. "No no no! This is all wrong! That didn't happen! I must have done something wrong!"
"Done what wrong?"
Twilight shot up. "Don't you see? I'm the only one who even remembers Starlight Glimmer! To all of you, she never even existed!"
"Again," Rarity said, "who is Starlight Glimmer?"
Twilight sunk low. "Who was Starlight Glimmer, you mean. If none of you remember who she was, then that means I've failed."
"Come to think of it," Applejack muttered, "who are you, for that matter?"
"And how are you doing that cool trick?" Pinkie added.
Twilight wasn't sure what Pinkie was talking about, until she felt a strange sensation in her hoof. Bringing it up to her face, she saw that her entire body was slowly becoming transparent.
"Oh no," Twilight breathed. "I'm fading from the timeline."
"Beg pardon?" Applejack asked.
"I tried going back and stopping a disaster from destroying all of Equestria. I thought I succeeded, but stopping it must have caused a chain of events that made me never exist, and changed history for the rest of you. The timeline is just 'catching up' to me now."
"Well you know what I think?" Applejack huffed. "I think this is all a bunch of—"
Applejack never finished her sentence, simply fading from existence in the middle of her rant.
Twilight scrambled backwards, pointing at the empty space where the earth pony once was. "Right there! Applejack just vanished!"
The rest looked at where AJ had been, then to her with puzzled expressions.
"Apple who?" Dash asked.
"The timeline must be affecting more than just me," Twilight deduced. "And there's no way I can stop it now."
She grimly marched forward, then looked down to Spike. "Spike, take some notes. I may be fading from the timeline, but I can at the very least record the process. And write down some warnings to any pony that would repeat my mistakes."
Spike dutifully produced a quill and paper, ready to jot down anything Twilight said.
"Right," Twilight began, bringing up one of her semi-opaque hooves, "I appear to be vanishing at a rate of twenty key-chronotons a second. At this rate, I will cease to exist within a minute."
Rainbow Dash began to ask what the hay a "key-chronoton" was, but as with Applejack, vanished halfway through her sentence.
Twilight grunted. "The rate of existential dispersal appears to be inversely tied to those most connected with the event."
"Wait a minute," Rarity began as she too began to fade, "who even are you?"
Twilight nodded. "Memory replacement also seems to be increasing exponentially. Are you getting all of this, Spike?"
Looking down to her assistant, she saw he had changed gender, but was otherwise carefully writing down her dictation.
"Also, parallel possibility is occuring."
Rarity faded away, leaving only Fluttershy and Pinkie. When they both noticed they were fading as well, Pinkie leaned over to Fluttershy with a sly grin.
"I heard about blending in with the scenery, but this is ridiculous!"
Fluttershy sighed. "Not now, Pinkie."
Within a second, they too had faded, leaving only the barely visible Twilight left in the Castle of Friendship.
In an air of finality, Twilight leaned down to Spike. "Spike, record this for all future generations. To any pony that would use time magic. Whatever you do, do NOT—"
And she was gone. The Castle of Friendship also disappeared, warping into the fabric of spacetime until Spike found herself standing in the center of the Golden Oaks Library, holding notes she didn't remember writing.
She looked around, scratching the back of her head. "What was I doing here?"