Twilight almost immediately set about checking the power of the disguise, poking and prodding the changeling with hooves and magic. Soon she disproved Shadows theory that it was just a visual illusion by pulling on his now much longer tail, to the pseudo-filly's discomfort. Further inspection of the fur revealed that there was actually skin underneath it instead of chitin, leaving Shadow to wonder just how thorough the spell he'd used was. Twilight was more than happy to find the answer to his question, a quick unauthorized check by the unicorn filly leading to an extremely girlish scream.
After a brief panic attack, stopped only by Twilight's assurance that it was probably the changeling race's special ability considering their name, she'd been running through what exactly had happened. The only thing she'd been able to pin down with certainty was that she'd unleashed a bit of magic from her horn, and she was concentrating on the unicorn when she'd been spooked.
'It may even be a subconscious thing.' She'd thought to herself. 'In emergencies where the changeling is startled they throw on the first form they can think of.'
Meanwhile, Twilight was floating paper all around her, writing notes on what they'd discovered and any running theories on the activation of the spell. The filly even started hopping around on her tippy hooves, giggling about how it would only make sense that she could also be any other race, even a Pegasus!
"Oh, you could fly anywhere you want to go! This is amazing!"
Shadow was less than enthusiastic however, and only wanted to be returned to her base form. The way to accomplish this, however, was not easy to find. First was the general dispel Twilight knew, which not only failed, but resulted in a spark of pain in both foals. Next was Twilight attempting to coach the changeling into breaking the spell, which would have worked if the spell was actually actively running.
"What do you mean there's no active spell?" She asked, a single hair springing up from her mane. "You're using a spell to keep your form different, aren't you? That's how transformation spells work, right? They change something and the power you store in the spell is how long it lasts! It said so in Basic Spells for Beginners!"
"I didn't use a unicorn spell, Twilight, it may not work by the same rules!"
"Magic doesn't work like that! It has rules, rules we have to follow! You can't just ignore them!" Three more hairs came loose.
Shadow slapped a hoof to her face. "You're trying to play Go Fish with a Chess set, Twi! I didn't say it doesn't have rules, I said mine may be different. Do pegasi have magic?"
The filly nodded. "They do, it's passive magic, though. They don't have horns to channel it with. It's all right here in Your Mana and You."
"So can a Pegasus use a unicorn spell?"
"No, that... would... oh."
"You keep trying to classify it by your rules, but maybe it doesn't run that way. What kind of magic are you calling this?"
The unicorn pulled a nearby book to her, flipping the book half her size to a tabbed page. "Transfiguration. The act of transforming one item into another. After the spell complete the.. oh.. after the spell runs out of power the object returns to its original form. Wait, if the spell was a one time transformation then it would be..."
Twilight trotted over to her rooms bookshelf, pulling a well-worn book from the top shelf. As she cracked it open, Shadow trotted up beside her.
'Mare, Ram, and Spinster's Dictionary? What the hell! What sicko thought this is funny?!?'
"Alteration, achievement, alot, aww, it's so fluffy! Ah, alchemy! 'The science of transforming one matter into another, most often used in the brewing of elixirs and tonics. Was the origin of the less popular science of chemistry, and started from the pursuit of unicorns attempting to change gold into aluminum."
"Gold into aluminum? Why would they do that? Gold's worth way more."
"It's rare where you come from?" The unicorn asked? "Aluminum is very hard to find, while gold is fairly common, and holds magic easily. Shiny said that's why the guard uses it for their armor. It's cheap, easy to mold and enchant, and with the proper spells, as strong as you want. It also doesn't weigh as much when some of those spells reduce the weight."
"Wouldn't it be cheaper to use, I don't know, iron?"
She gave him a confused look before flipping the page to I. "Iron, a rare metal that repels all but the most powerful spells. Mostly assumed to be extraterrestrial in origin due to its incompatibility with the world's natural magic field." Finishing the definition, she looked at the changeling. "Why would you make armor out of that?"
Shadow went to retort, but fell short, imitating a goldfish for a few moments before closing her mouth with a click. 'I remember hearing about iron being the bane of fae, but this is ridiculous. Does anything I know even matter anymore?'
"Okay, never mind. Look, say this magic is related to achemy. How does that help us?"
"It's simple!" The mage to be said with a smile. "Wait, no it's not, but it does simplify the problem. If there's no spell keeping you this way, it means that this is currently your actual form. That means you can reapply the spell to transmute yourself back!"
"Awesome." Shadow deadpanned. "Any idea how I cast the spell in the first place?"
<-(0)->
Being seated at the dinner table while still looking like Twilight, with said filly to her right and Shining to her left, was not how Shadow planned on spending her time. The first few minutes of dinner confirmed her fears; the transformation was only physical. The ponies talked, and she didn't understand a word. So she nibbled idly on the meal, a strange dish that she couldn't seem to identify despite her best efforts, and tried to decipher what was going on based on Twilight's responses. The table wasn't any more welcoming than it was earlier, in fact Shining armor was downright furious with the now-filly changeling, probably seeing it as the next step in Shadow's evil plan to replace his sister. There was just no pleasing the guy. The mother, Twilight Velvet as his only conversation partner had introduced the mare from earlier, was at least doing her best to be hospitable, while her husband, Night Light, just watched him, fear creeping into his eyes as she met the older stallion's gaze.
Turning to the unicorn filly, she noticed Twilight looking around the table uncomfortably as well. She wanted to say something to her, to jump over to Twilight's seat and just sit next to her, anything to comfort her. But her presence was what was causing this friction. Her being there was why the brother was glaring, the guy's fury almost reaching a point of being considered hot for the filly. The parents weren't as volatile, but they weren't comforting either. That wasn't what Shadow's friend needed right now, she needed certainty, she needed someone to give her a hug, someone to tell her it was all going to be all right! She wanted to do it, she wanted to do it so badly.
But looking around at the confusion, the fear, and the anger, she couldn't. Because for the first time in so many years, she felt exactly the same way Twilight did. For the first time in years, Shadow wanted nothing more than to find a place to hide, curl up in a ball, and cry. It didn't help that their emotions seemed to feed into each other if they were synchronized. In this way, it made things worse. The second she'd been certain most of them were finished eating, she excused herself, almost running from the table. She distantly heard another voice her exact words in the same voice, and could almost feel the filly darting after her, intent on reaching the same goal. Eventually they made it, Twilights bedroom being mentally marked as a safe spot for the two, despite Shadow only having been there twice. They climbed up on the bed, wrapped themselves in the blankets, and cried in each others grip.
Twilight cried in confusion and fear, not understanding her parents reaction to her new friend, even though the Princess said it was okay. They'd always told her to trust the princess, so why wouldn't they? Worst of all had been her BBBFF, he just looked so mad at Shadow. The changeling didn't do anything to her, if anything Twilight had hurt the colt! Why was Shiny so mad at Shadow?
Shadow cried from her frustration, her inability to understand the situation, and the horrible pit in her stomach that formed thinking she'd somehow messed things up royally for the family. The filly loved her family, and they loved her. Now here comes this random alien creature that gets linked to their daughter by accident and they have to deal with it. It was clear they were doing just that, but despite having no practice reading pony faces, their emotions were plain as day to her. Fear, anger, disgust. She was certain the only thing keeping the white stallion from lashing out at her a second time was the fact that his sister would feel a phantom impact as well. Twilight had spoken so highly of Shining Armor, she loved him with all her heart, seeing him like that hurt her deeply.
And what hurt Twilight, hurt Shadow. She knew this link was the cause her sorrow and fear, but to be reduced to a sobbing mess so easily hurt what little of her pride she had left. It hurt her pride, and she could do nothing about it. Shedding more tears of impotence, she clung tighter to her comrade in misery, the two eventually crying themselves to sleep.
<-(0)->
Time passed, eventually finding the two foals curled up amidst the blankets of the filly's bed. Shadow assumed it was approaching sunrise by the time she actually started moving, but had no way to know without asking Twilight. Staring out the window at the night sky, she just couldn't find the motivation to do anything. This was supposed to be a time of recovery, time to learn about a new world she'd gotten stuck in, not a time to create a rift in a loving home.
She needed to learn how to use her magic as soon as possible, if only to lessen their impact on each other's emotions. Not only that, she could finally go back to being male again. Unsurprisingly, a full nights sleep hadn't removed the effect of her transformation. It was both a curse and, though she loathed to admit it, a blessing. She really wanted to be free of her current form, but on the other hoof, she now knew she wouldn't end up losing her disguise if she ended up falling asleep or got knocked out. That was good, because she liked sleeping in.
Managing to detach herself from her clone, she focused on the written word, delighted by the fact that the pain of the language-switch didn't seem to hurt too much anymore, as it meant she didn't wake up the sleeping filly. She quickly ran a hoof along the spines of Twilight's collection, finding the basic magic spell books the unicorn had been reading to her the day before. The sooner she got her magic under control, the better things would be all 'round. Taking one last glance at her collection, she dove in.
She read sentence after paragraph after chapter, trying every exercise in the book until she got it right. She started levitating things in her magic, more than she thought she reasonably should have been able to. She lifted things up based on weight, once more lifting so much more than the book predicted for a first time caster. Why? Why did she have such a large source of magic? Where was it...
Her gaze turned to the sleeping filly. It was her, Shadow was certain of it. The surge had been enough to pull her between dimensions. Twilight's surge had been enough to scare trained soldiers into doing everything they could to neutralize her. What else had the filly done with such a large source? What else was she capable of? The book said one's source would only grow with age, and she already was so powerful, how much stronger would she get? Would the changeling's presence increase that strength, or would she dampen it? Would her tapping into the unicorn's mana actually harm her? There was so much she didn't know, and with such things, she had a feeling only Celestia would be able to answer these particular questions, if answers were to be found at all.
After nearly two hours of combing through the books, doing everything she could to fine tune what little control she had over her magic, she decided to take a break, heading to the bathroom for a drink. Walking into the nearly immaculate room, she quickly used the stool to take a look at the top of the sink. She grabbed a cup with Twilight's mark on it, and downed two full glasses of water, before refilling the glass and levitating it along with her back to the filly's room. Just before she was back in the bedroom, she turned, ears perking up at a series of soft nickers directed at her.
Her mood dropped considerably at the sight of the white unicorn, as did his, the smile vanishing the instant he saw the greenish hue of the aura on the cup and her horn. Shadow sighed, setting the cup down lest she drop it even as the stallion came closer, spewing gibberish she couldn't hope to understand, demanding answers too, if his inflection was to be trusted. Closing her eyes, Shadow focused again, this time attempting to pull the spoken word from her twin.
"..think that just because you look like her, you can use her things?" The stallion said quietly, trying to avoid waking the rest of the household.
"I was thirsty, and figure she will be too. Is there a problem with that?" Shadow said, bringing her attention fully to Shining Armor.
"And now you steal her language again. I don't know what spell you put on the princess, but.."
"That, ass-hat, is called entrapment. You get angrier as I don't answer, so I swapped with her to answer you. Then you get angrier when I try to actually answer you. And spell?" Shadow exclaimed. "I didn't even know what I looked like until I had a chance to look at myself in the mirror after that nap! I didn't even know magic was real until two days ago! And you think I put some type of spell on someone who's been around for centuries at least? Possibly longer than my species' recorded history?!?"
" Listen here, bug, I'm in the Royal Guard now, and it's my duty-"
"Oh yes, the wonderful Royal Guard." Shadow muttered, rolling her eyes. "I bet someone who punches little kids would fit right in with them. You know, considering they threw your little sister into a cage."
"What?" Shining asked dumbfounded. "A cage? They would never do that! She's just a filly!"
"Ask her yourself when she wakes up. They threw us in cages and put some weird rings on our horns. The Princess didn't seem to happy about it." The changeling grinned. "I expect you'll hear something about a demotion or five somewhere down the line, maybe even a public apology to your parents and sister for the psychological trauma incurred in his care."
The stallion looked ready to object, torn between loyalty to his vows and loyalty to his family, when the changelings focus went form him to the door, now cracked open, a purple head peeking out into the hallway. Seeing a chance to learn the truth firsthoof, he slowly walked around the bowing alien wearing his sister's form, before leaning in close to his sister.
Turning around, Shadow watched the exchange. She wanted to know the other side, but knew Twilight needed her brother back. Nothing would trump his protectiveness from the changeling but the knowledge that his little sister went through something horrible recently.
The stallion said some things to the filly, earning a slow, teary nod, before he scooped her up in a hug. He started saying comforting things to her and petting her mane, and the Twilight just hugged him, telling him how scary it was, how nopony would listen or help her, how everypony seemed scared of her.
Shadow coughed, catching the attention of both unicorns. "Twilight, can I tell him one more thing? The glass over there is for you, by the way."
The filly nodded, pointing to the asking her brother to let her get a drink. As she drank, Shadow once more swapped the languages, each time becoming easier for the two of them.
"I have one goal right now, Shine. Keeping her from sending my own emotions into a tizzy. I'm normally a pretty calm guy even in the strangest situations, but not only this beyond anything I could imagine, when your sister starts to panic, so do I. But it's two ways. When I fear something, she picks up on it as well, and if we're both feeling uncomfortable? Things like last night happen." The changeling explained. "I don't understand how it works, but we can spiral pretty fast from what I felt. Just, I know you don't like me, you don't have to, but swallow that anger for her. For pity's sake, an effectively immortal princess told you I'm harmless, a princess Twilight said you guys told her to trust. Why can't you do the same?"
"Will you stop stealing Twilly's language?" The stallion finally asked, looking at the not-Twilight.
"I'm not stealing it, geeze." The changeling said in a huff. "Still, no Shining, I plan on learning the language as soon as I can. I've never allowed myself to be called a parasite for mooching nor do I allow myself to take advantage of others' kindness." Shadow then frowned. "I may need to find someone else to teach me though. Twilight won't be able to teach me much when it comes to pronunciation, since I hear her words in my own language."
After a moment of thought, the stallion sighed. "Fine, but if I find out you so much as harmed a single hair of her mane-"
"I get it, dude, you're talking to a fellow older brother." Shadow said, before closing her eyes and holding a hoof raised in oath with her other over her heart. "Heaven have mercy on those who harm the younger siblings, because an older brother will have none."
The stallion raised an eyebrow at the oddity of a small filly saying such things, but nodding in agreement. Taking his sister in one more hug and whispering a goodbye, he walked down the hallway, still uneasy, but not sure how to remedy the situation.
"He doesn't look so angry anymore." Twilight said, watching him leave. "Why was he so mad at us?"
"It was me he was mad at, or rather about." Shadow answered. "As much as I hate it, this is probly going to take time, and it's gonna be painful until we either find a way to cut this link and send me home, or... or everyone learns to adapt."
The filly nodded, sidling up beside her mirror image. " 'Probly' isn't a word, and neither is 'gonna'."