The Invasion
Princess Twilight Sparkle trotted down the hallways of Canterlot Castle on her way to the library. She did have three large bookcases in her room, but somehow she had gone through all of them in only two months. She turned a corner and almost ran into another pony! The golden unicorn spread her wings in alarm…wait…
"Hey, who are you? There are only four alicorns in Equ-" she was cut off by the soothing touch of the alicorn's touch on her shoulder. She felt a spark run through her body and she shivered for a moment before looking up to see… Sunny Daze! Her childhood friend!
"Feel better now, Twilight?" Sunny Daze asked.
"Thanks Sun, I don't know what was wrong with me to not recognize you!"
"Sisters forever; Alicorns together!" Sunny Daze smiled cheerily
"I'm going to the library, wanna tag along?"
"Sounds fun!" The two alicorns trotted through the halls and bumped into Princess Celestia. Twilight was amazed. A castle as big as a small town and she manages to run into two of the four alicorns that live here! Next she'll find Cadence off in the kitchens!
"Ah Twilight, I was hoping to- Who is this?" Celestia looked at Sunny Daze with slight distaste.
"Princess? Don't you remember Sunny? We have been friends since foalhood! She was your student as much as I! We ascended into alicorns together, remember!" said Twilight with amazement.
"It's me, Princess, don't you remember me?" Sunny Daze reached a hoof out to Celestia but the white alicorn stepped back out of reach.
"Twilight, I required your help in the drawing room. It is to do with the elements of harmony so I am afraid Sunny Daze cannot come. Sunny, could you please return to your room? I have need to speak with Twilight in private." There was no hiding the fact that the Princess's tone was far harsher than before. Sunny Daze narrowed her eyes slightly at the Princess, just long enough for Celestia to see, then brightened up immediately, nodded and trotted back to her room.
"Princess? What's wrong with the elements?"
"Nothing. I simply needed to get you away from her."
"Sunny?"
"Her name is not Sunny. She is not an alicorn."
"Oh princess, she ascended from being a unicorn just like me! Does that mean you don't consider me an alicorn either?"
"No. She is…a different matter. Up until this morning she did not even exist."
"B-But I remember her. I remember everything, childhood memories, studying under you, ascending, everything!"
"And who remembers such things so clearly from so long ago? Certainly not me. Even if I truly focus some things are still blurry. Your memories are as crisp and fresh as though they had been made this morning…because they were."
"She is real!"
"She is a shapeshifter."
"She is not a changeling!"
"That is one thing she is not." Twilight was taken aback by the princesses words.
"B-But you said…"
"I said shapeshifter. She is far worse than a changeling. She appears, takes on a random form, then alters memories via touch to blend in to her environment." Twilight suddenly remembered the gentle touch on the shoulder from not ten minutes ago.
"…the spark…"
"Twilight?"
"She brushed my shoulder this morning…I felt…a spark…running throughout my body…"
"That was her altering your memories. They are similar to changelings, in a way, but they do not just feed on love, the live off attention."
"What do you mean?"
"Well, while a changeling will feed off love, making you weaker, this creature simply melds into your life and instinctively begins to change memories and alter personalities."
"W-What is she?"
"A creature so old and mysterious that nopony, not even I, knows the true name of what she is. We call them Mary-Sues though, the same name as the first one given in recorded pony history. She was trying to pass herself off as another sister of a large family of earth pony rock farmers. Stuck out like a sore thumb being so pink. Anyway, she disappeared, but since we use her original name for the species' name, she cannot truly disappear. Luckily one of the brothers had been working in a full body boulder protection suit. She never stood a chance of touching his skin. He started to keep it on at all times and documented her, and it's thanks to him we have the information about Mary-Sues that could be translated from Olden Earth into Modern Equestrian."
"Wow. So that' why you didn't touch her before!"
"Indeed. Twilight, the next part of ridding yourself of her is much harder. You must forget she ever existed."
"Can't you just cast a memory spell on me?"
"I am afraid not. These creatures are immune to such things. Even if I wiped everything from your mind, she would remain, and eventually consume all of your mind and soul, and you would do nothing but chant the name she gave you over and over, because the only thing left in your mind, the only thing able to be in your mind, would be her. And she would thrive, becoming more and more real, and only when you die would she ever be destroyed." Twilight shuddered at the thought of this. That was a fate worse than death. It was a half-life, alive but not living.
"So…How do I forget her?"
"Distract yourself. Focus yourself on one of your passions. Perhaps reading? I could set you a research task." Twilight smiled.
"That sounds perfect."