Ponyville, Twilight's room
That same evening, as Twilight and Spike were cleaning up the library, Spike asked about the new pony Twilight had met.
"So, what was her name?" he asked, re-shelving the last of the books.
"Tattered Wing," Twilight responded.
"Hmm, strange name. So, she spent the entire day reading these magic books?"
"Yep. However, I would have thought that Pinkie would have thrown a party for her, seeing as how she's new."
"Well maybe Pinkie's just- Urp!" Spike was cut off as he burped out green flames and a message from Princess Celestia.
"My faithful student, Twilight Sparkle," Twilight read aloud, "Soon after your brother's wedding, my sister captured a changeling still inside the Canterlot borders. After much deliberation, we have decided to have you conduct a study on him. Princess Luna should arrive with him soon."
"Ohmygosh, Spike! Do you know what this means?"
"That I'm not going to get any sleep for the next month?"
"Of course you are. Owloysius can take notes during the night shifts. Right, Owloysius?"
"Hoo." the pet owl responded from her perch by the window.
"You're going to be writing the notes, I thought I just made that clear." Twilight said, giving the owl a quizzical look. Instead of giving another reply, Owloysius just buried her head in her wing. "Hmm, anyways, this means that I could be writing notes that could be put in a book that gets put in the Royal Library! That's what I've always dreamed of, aside from being Celestia's best student. There's one thing that bugs me though..."
"What?"
"Cadensa's and my brother's spell should have ejected all of the changelings from the city limits. I wonder how one managed to stay inside."
Canterlot, Three days earlier
Two fillies cowered in front of him as he loomed over them. He was going to do it, he was going to drain the both of them of emotion, but... The changeling hesitated, This seems wrong... No, it's not. The Hive-mind said to feed, so you feed. It had always been this way for the changeling, two different thoughts occupying his head at once. There was no reasonable explanation for his condition, he was just a changeling that argued with it's self. A searing headache interrupted his conflicting thoughts. Then, a flash of bright light caused him to look back towards the middle of the city and see a giant pink orb start quickly expanding from the chapel, sending his fellow changelings flying from the city. Oh, horse feathers. The changeling tried to take off and escape, but the love wave caught him in mid-flight and sent him (or rather, his face) smashing into a series of objects. Through the pain, of each impact, the changeling randomly listed each item that came in contact with his face. Sign, sign, sign, sign, sign, sign, sign, anvil (How did that even get there?), sign, sign, sign. sign, sign, sign, sign, sign, sign, hanging piano, sign, sign, sign, sign, and finally, solid brick wall. Thud!
As the wedding between the real Princess Cadensa and Shining Armor progressed, Princess Luna was walking around the city with two royal guards, surveying the damage to the city.
"Princess Luna!" one of the guards called from down the road, "I think you would want to look at this!" The princess walked over to where the guard was hovering and saw a long line of destroyed store signs. She followed the line of destruction and also spotted a an anvil with the indentation of a changeling face in i and a piano broken the same way as the signs. The line of destruction ended at a changeling half buried in a wall.
"Guards," Luna said to the two stallions, "remove thy changeling from yonder wall."
"Yes your majesty!" The guards picked up some pieces of wood and proceeded to pry the changeling off of the wall.
"What beith the status of thy changeling?"
"It looks dead your highness, and you're doing it again..."
"What beith that we art doing that- Oh, I was speaking in Traditional Canterlot again, wasn't I?"
"Yes you were. Now what should we do with this- Hold on, I think it just moved."
"What?" the other guard said, "That can't be possible. Nothing could survive that amount of torment... Sweet Celestia, you're right! It just twitched!"
"Guarding Light," Luna said, addressing one of the guards, "bringith thy- I mean, put the changeling in a prison cell for now. You," she said pointing to the other guard, "come with me. We must finish the inspection of the city."
"Yes your majesty!" Both guards said at once. As Luna and the other guard walked away, Guarding Light picked up the changeling and carried him off towards the prison cells.
Hey, moron, wake up. The changeling stirred slightly. I'm talking to you, you piece of cow dung! Get up!
Sweet Chrysalis... "I'm up already, what do you want?" the changeling said as he got up, holding his head in pain.
"Quiet in there!" yelled a voice from outside the cell door, "The prisoner shall stay silent!"
"What the? When'd I get in a prison?"
"I said QUIET!"
Hey! You broke me! What'd you do to my body?!? Your body? This is my body! And what do you mean broke? The talky thing! You must have done it when you threw yourself in front of those signs! What? That was not my fault! That stupid love wave forced me into those! Unless you think that was my fault, too. Of course it was! Then why didn't you take over and get us out of there? ... That's what I thought. "Hey, you, there!" the changeling called to the voice outside the cell. "Why am I here?"
"Celestia, help me, if you don't shut up, I'll - "
"You'll what?" asked another voice.
"Princess Celestia! Princess Luna! I didn't expect to see you here so soon!"
"Never mind that. How is our little changeling doing?" The changeling watched as a tall white alicorn came into view outside the cell door. Using her magic, she opened the door, allowing herself and another alicorn, probably Princess Luna, to enter.
"Sister, I don't believe this is wise ... "
"Hush, Luna," the white alicorn said, revealing herself to be Princess Celestia. "Now, how are you today?" she said, addressing the changeling.
"Ummm, well- BUCK OFF!!"
"YOU DARE!?!" Luna raged.
"Calm down, sister. This changeling doesn't seem to be himself."
"Oh, shut up, you old crone! Gah! I didn't mean it! I'm sorry! Quiet, you! So come down to torture me or what, hags?" His speech was cut off as Luna's hoof came into swift contact with the changeling's face.
"Wha- Luna! Why did you do that?"
"Yonder changeling appeareth to need-"
"AHEM!" One of the guards cleared his throat.
"It seemed that the changeling needed that."
"Ugh, ow ... I think that'll shut him up for a while," the changeling said, holding his face.
"He? Wasn't that YOU talking just now?"
"No, well, yes, err, sort of?"
"Seems like multiple personalities," Luna said. "Remember the guard who had that same problem, sister?"
"Oh, yes. That was slightly problematic. Good day, changeling." With that, Celestia exited the cell alongside Luna.
"Well, Celestia seemed nice," the changeling said to himself, once the princesses were gone.
You idiot. Ugh. Don't you know what they do to changelings here?
"No, do you?"
"Well, umm, no. Shut up, it can't be anything good! I mean, we just attacked their main city! They can't be happy about that."
"Oh, I didn't think about that ... So what do we do?"
"First, we need to take out those guards.
"You mean, those two?"
"Yes.
"I think the changeling's talking to himself!" whispered one guard to the other.
"Who cares? I just want to see how long it takes to break it."
"Come on. You don't need to torment him. What's he done to you?"
"A whole swarm of them just attacked the city, two days ago! That's enough of a reason for me." The changeling stuck his head out through the bars.
"Do you mean I've been knocked out for two whole days?!?"
"QUIET, YOU!" roared the second guard, as he struck him across the face with his javelin.
"Son of Tartarus!" the changeling yelped, holding his face in pain.
"That'll teach it."
"You didn't have to be so harsh to him. He was just asking a question." The changeling lost the rest of the conversation focusing on his face's pain.
Now will you just drain them already? Ugh, now that you mention it, I do feel kinda drained... Good boy, now turn them into lifeless husks so we can get out of here. Well, when you put it that way... DO IT! Gah! Fine!