A Guard and Two Changelings
The sun shone brightly above the proud, magnificent capital city of Canterlot. Ponies roamed the streets, bouncing between shops on this gorgeous Friday afternoon. Much of the city was booming with tourism, as spring had sprung in Equestria.
Out and about walked along Silent Knight, lieutenant in Princess Luna's House Guard. His brilliant white coat gleamed in the light of the sun, along with the freshly polished dark blue and purple armor he wore on his chest, hooves, and head. Rather than the slit-eyeball for an emblem on his breastplate was Princess Luna's cutie mark, a moon surrounded by a couple of white dots for stars. Above all, his helmet resembled that of a city guard's, who's helmet included a mane piece on top, in which it was a night-blue with minor highlights of a slightly altered, lighter shade of blue mixed in between.
The pegasus did not normally set out for patrols, this occasion being to enjoy the post-Winter wrap-up weather. Part of which it was, at least. Overall, it was about missing the normal guard patrols before his big promotions into her highness' house guard. The further time he accumulated only left him in an office, or standing in the princess' personal quarters within the Canterlot Palace. The only times he would ever leave were special missions or escort duty.
Unfortunately, for him, he came unaware that today was just not the best day. In the direction he walked and hidden by the shadows of an alleyway waited a jet-black, blue bug-eyed pony. His hooves up to his knees were riddled with holes small and large, as well as two large fangs in his mouth that hung down. The pony's magic granted him the ability to shape-shift into anypony it saw. Its intentions were to kidnap a guard to replace in preparation for yet another, hopefully successful, attack against Canterlot, a plot to allow his queen to take control of the whole country.
Striding past and whistling to himself, Silent Knight spread his wings to take in the warm sunlight. From the base up to the tip of his wings shifted to a royal blue matching his mane and tail color, making him stand out against the rest of the guards. The changeling watched as he approached, not immediately realizing who he was for the first few moments after he had tackled and dragged the poor Lunar guard into the alleyway and knocked him out cold with a hard blow to the forehead.
What seemed like just a couple of long minutes later, Silent awoke from his sudden slumber. Rather than the brightness of the afternoon was the darkness of a cold, rocky cave. Except where he woke was not cold, nor rocky. Instead, the floor was squishy and green with a slight glow to it. Silent soon came to realization where exactly he was the second he caught on to himself standing upright, somehow.
He could not move either, much to his surprise. Glancing down to his hooves, he saw the two of his forehooves standing in a cold, sticky, green goop that reached up past his fetlocks. It told him who was behind it as well. Only changelings trapped their victims in such slime. It could be formed to be used as other ways to keep a pony in place aside from sticking them to the ground. Silent pulled up on his hooves a few times in an attempt to break the sticky hold of the goo, though it was to no avail.
Silent's heart pounded heavily against his chest and his breathing quickened. Looking up from his hooves as he squirmed them around, he immediately saw multiple green transparent pods with shadowed figures trapped inside, motionless. Upon further inspection as his vision cleared from being knocked unconscious, he saw they were all guards. Guards that had gone missing over recent weeks. They were all here.
Now in a panic, Silent returned his focus to his hooves, trying ever so desperately to escape the trap before he could be put in a pod next. That was, until, a voice from in front cleared its throat. He froze, gaze moving upwards and meeting that of a pine green-maned changeling, standing and staring curiously just a couple of feet apart.
He lowered his hoof and stood completely still, heart pounding even quicker than before and chest heaving at a rapid pace. This was it. He was going to be put in a pod, never to be seen again.
"SSSSilent Knight?" The changeling spoke.
Silent didn't reply, instead eyeing the creature cautiously and nervously.
"There issss no need to be afraid."
No matter the changeling's efforts to calm him, Silent Knight felt fear sweep over him like a gust in a storm. The changeling, after a few minutes, took a seat before the slightly larger pegasus, smiling warmly to his captive.
"What... do you want with me?" Silent finally said.
"Nothing important. I was ssssimply doing my job for Queen Chrysalissss. I am here to check on your condition."
"Aside from a headache..." Silent gulped. "I am fine."
"Headachessss are to be expected after hitssss to the head. Any pony sssshould know that."
"Right... Of course." Silent nodded once, then tugging up on his hoof.
"There issss no need for the ssstruggle. You will not be leaving any time ssssoon."
"Let me go. Let all of us go. What is this even all about?"
Tapping his hoof gently on the gooey floor, the changeling replied, "That issss none of your concern."
"I would appreciate being able to know what you are going to use me—us—for," Silent eyed the changeling again.
"Again, that issss nothing for you to—"
"Hey!"
"Uh oh."
Standing across the room was another changeling. It was exactly like the one before Silent! What was going on? They looked exactly the same.
The one standing in front of Silent turned around, eyeing the other as it approached, baring its fangs and hissing.
"What issss thissss all about?"
"Get lossst, Storm."
The second changeling, Storm, hissed once more. "You do not tell me what to do! Why are you looking exactly like me?"
"Honorary replacement. I'll ssssay it again. Leave."
"Or what? What will you do? You are weak!" Storm took a step forth, pressing his muzzle closer to the unnamed changeling's.
"Do you want to know?"
"Yessss, I would!"
Before any reply could come from the supposed impostor, a blast of magic struck Storm, sending him flying back into the wall, the softness of it bouncing him straight off and back to the impostor. He yelped in pain and pushed himself up, hissing loudly at the other, while Silent Knight helplessly watched.
"Do not... do that... again." Storm threatened.
The impostor walked closer to him, spreading his hole-ridden bug wings. "Or what?"
Storm's horn lit up in a sickly-green aura, preparing to shoot at his impostor. The moment he did, the other teleported out of the way, the beam inadvertently striking Silent's hooves. He yipped as the magic burned his forehooves slightly, but freed him of the goop. Silent spread his wings to fly out, only to be stopped by the goo on his hinds still holding him in place.
The impersonator reappeared in a bright blue flash behind Storm, chuckling darkly and giving a fangy grin toward Storm. He growled and whipped around, horn still lit and firing another quick beam at the clone. Once again, the impostor teleported away, the magic striking the wall and leaving a burn mark that emanated some smoke.
To his side appeared his clone, now cackling evilly. "You'll never catch m—"
The clone was suddenly struck down by a large blob of goop that smacked hilariously into his face, covering it completely. He now lay on the floor, out like a light. Storm blinked a couple of times, turning to look at the captive Lunar guard and seeing him shaking his forehoof, trying to get some of the green substance off after having thrown a large amount of it at the clone. Instead, some flung up and stuck to his muzzle. With a frustrated sigh, Silent's gaze moved up to Storm.
"He was annoying me, too." Was all he said.
Author's Note
My apologies as well if Silent is out of character here, but I wanted for him to be kind of a nervous wreck for this story. 
Also, you guys tell me! Does Silent get freed and live, or is he put away in a pod to be harvested for his energy and strength?