It didn't move. It hadn't moved for hours by then. Nary a twitch had come over its black body, undisguised, sitting silently to the side of the Ponyville Library door, throughout the time it had sat there. The changeling felt no need to move—its mind was cold, precise, and focused, and the only purpose that guided its mechanical thoughts was the completion of its queen's will. It did not feel boredom at the wait. It did not feel proud that it had been selected for this task over other changelings, though the decision had been motivated by its skills and its strength. It did not feel worry over the fact that failure would mean, almost certainly, death or lifelong imprisonment. It did not feel eagerness at the prospect of completing its task, which would go unrewarded, though a reward would not have made it feel any more emotion. The changeling felt nothing.
Mentally, it reviewed its commands, without contemplation or particular concern. Chrysalis had been clear and simple. She had not spoken directly to the changeling, as direct speech was unnecessary between drones and their queen, but the shared thoughts had been perhaps more clear than any verbal communication could be, despite being little more than sudden feelings and vague strings of thought with no possible origin but the foreign mind of the changeling's queen. New memories of a unicorn with a purple coat and a simply styled mane of darker purple with a pink stripe in it. Vague flashes of voice associated with the images. Random facts picked up from conversations with a stallion named Shining Armor of significance to a plan. Rage. Contempt. "I should kill her." "She ruined my plans." "How better to get back at them—at all of those who cast me back to this wasteland in disgrace—than to destroy what they hold dear." "I'll send a drone. If it fails, I'll send another." The changeling had known what to do as soon as it detected those foreign memories and feelings. It always did, when such things came.
The changeling had done a shallow level of research on its target before acting. It had known from transferred knowledge vaguely where the mare lived, a town called Ponyville. It had traveled there, visible to all as only an unfamiliar pony. Almost immediately, it had encountered a pink, energetic mare who had seemed excited by a new arrival being present in town. With a soft, polite voice, the changeling's disguised form had asked if the town had a library, which the pink mare had eagerly answered "yes" to, before describing said structure's location, qualities, and denizens in a rapid stream of language. She had then left to go prepare for some sort of welcome party. The changeling left town, changed appearance, and briefly, without anger, relief, or disappointment regarding itself, assessed its behavior as having been unlikely to produce positive results and the actual happenings as fortunate. It would adjust in future tasks. Risky tactics were not advantageous to the whole statistically; they increased risk of failure. Failure would result in being caught, from which would likely occur death or imprisonment. Either would remove a worker from the resources of the hive. That was an unacceptable consequence, unless it served a purpose for the whole.
It had re-entered shortly after, in a different form again, and gone immediately to the library. It had found a "Vacant—At the Park," sign hung on the door, words written neatly on a piece of paper. The changeling had entered the building. It confirmed it empty, and then sat down besides the door, dropping its disguise to conserve its magical energy for when it would be of greater benefit to use.
It did not move for several more hours, until it faintly heard the sound of hoofsteps coming gradually closer and closer to the door. It stood soundlessly up, rising with a sense of relaxed indifference. Silently, green flame swept up its body in a fast wave. Its appearance changed to that of a pony, a mare with a pink coat and a short mane of light brown. It looked to the door as the door of the library swung open. Its target walked in.
"Hello," the changeling said, again in a quiet, polite voice that spoke of a shy disposition. It glanced down at the ground as it said this, in imitation of an embarrassed manner. This would gain either contempt or empathy from most other ponies, either of which normally placed the changeling in a beneficial position to act. It presumed the tactic would work here.
Twilight looked at the changeling with confusion. "Oh. Uh, hello."
"Did someone go in past the sign?" said a younger male voice in a somewhat smug tone, one that implied casually a kind of disdain for the 'someone.' A small dragon entered after Twilight. Twilight's horn glowed, and the sign placed on the door was brought inside in a telekinetic grip. The door swung closed behind it.
"Shh, Spike. Don't be rude to- Uh-" Twilight looked back from her assistant to the changeling. "Who are you? I don't believe we've ever met."
"Meadow Breeze," it said quietly. "I'm just visiting town. I heard Ponyville was a nice, natural place, and, well, uh..." It made itself drop off awkwardly.
"I see," Twilight said, seeming to relax a little at the false explanation. "Well, what did you need at the library? You must have been pretty eager to get it, to go inside and wait." The small dragon gave a look of bored dismissal as she said that, and walked up the stairs on the wall to enter one of the bedrooms above. The changeling made note of his leaving. Seconds later, it heard a door close above.
"I wanted to get some poetry books to read. See if there were any I hadn't read here..."
Twilight smiled brightly. "Wonderful! I admit, I don't read too much poetry, but I'm sure we'll find something for you to enjoy while you're here. Ponyville has a rather nice library." The unicorn turned, apparently heading to a shelf. The changeling moved, its disguise dropping. It made little sound, considering the speed it moved with. In a single bound, it was beside her, its natural mouth unhinging to open wide, fangs seeking her neck as her head turned to look back. The teeth sunk into the soft tissue, and the changeling immediately dragged its head back with a ferocity and strength that seemed contradictory to its bulk, the sharp inner edges of its teeth cutting through flesh like little black razors. Twilight gave a small sound of surprise. Her eyes widened in fear as they looked back at the hard lines composing the black, insectoid face looking without feeling into her eyes as she died. The changeling's mouth opened again, shifted position slightly, and snapped again shut.
Her blood ran over its tongue and down its throat as it tore at her. Twilight gave several more quiet, desperate sounds, as her body started to give weak shudders. Her eyes darted desperately about, unfocused, seeking a means of escape that did not exist. The changeling bit again and again. Gradually, Twilight's resistance died. The changeling waited patiently. Eventually, as seconds slipped by, she grew still. She did not fall, suspended over the wooden floor by the changeling's powerful grip on her neck. It waited another minute to ensure she was finished. Then, slowly, it lowered her to the ground. It checked her heart. Stopped. It listened upstairs to see if the dragon had noticed anything. To its surprise, the dragon didn't seem to have. The door that had closed didn't open. The upper floor was as still as the bottom.
Calmly, the changeling changed back into Meadow Breeze with a sweep of green energy. The mare looked as she had before her brief disappearance. She displayed none of the blood coating its teeth, nor did she show the thin scarlet streaks on its neck where blood had leaked and ran down from the edges of its mouth. Silently, the concealed changeling walked silently out the front door of the library. It walked out of town, past ponies casually chatting, past ponies selling their wares, past a pony reading a book with an intense look at the table of a cafe. It encountered no resistance. It felt no happiness or sorrow at this fact. It felt no satisfaction that its mission was done. Once it was outside the town boundaries, it dropped its disguise. It unfurled its wings and took to the air, flying back to the distant hive. It would have to fly for days to reach it. Then, it could receive a new task, which it would do without complaint or expecting recognition. For the hive.