It was perfect.
Rainbow Dash hid her grin behind her hooves. She hid her hooves - and the rest of her, for that matter - behind the stairs. She had been trying so hard, so very hard to come up with a good prank to pull on Twilight.
Oh, she'd pulled pranks on all her friends before - barring Fluttershy, of course - but Twilight was a Princess now. While Rarity might have been the first to fawn over being close friends with royalty, Dash had just taken a while to really acclimate to the idea.
Twilight was a Princess.
Twilight was also her friend.
You weren't supposed to prank Princesses. Like, ever.
But friends are always fair game, at least once.
[Except Fluttershy. There are some lines you just can't cross. Ever.]
When Rainbow Dash had put two and two together and realized that she could prank Twilight - Princess Twilight, and that meant she could prank a Princess, well, it's obvious that she had to do it.
But Rainbow was a mare of high standards. If she was going to pull a prank on royalty, then the prank itself had to be royally awesome.
That's where it got hard. A good prank gets a crazy reaction from the pranked without causing real harm to anypony. If you don't upset or startle the pony enough, it's not a prank. But if you go too far, it's just being mean. And even though Twilight wasn't as sensitive as Fluttershy, she could still be pushed over the edge more easily than the average pony. After the Smarty-Pants incident Rainbow Dash had to write off any future prank plans involving telling Twilight she was overdue for anything ever.
So she'd had to figure out just what she could do that would make Twilight freak out without, you know...freaking out.
It had to be something big. Dash thought and thought until she came up with a brilliant plan - she'd push Twilight right to the edge, then swoop in and reveal the prank before she fell. That meant, though, that whatever the prank was had to be completely harmless in reality, but make Twilight think it was incredibly awful. That way, she'd nearly panic - just nearly - and then when Rainbow Dash explained it was all a hoax, she'd be too relieved that it wasn't real to be really angry. Oh, sure, she'd probably yell a bit and make a speech about trust and friendship and blah blah blah, but as long as she didn't make the town crazy or burn down the library -
And that's when it hit her.
Twilight loved that library, like she loved the books it held. Rainbow Dash could make it look like something awful happened to the Library, and Twilight would freak out. It would be perfect.
Well, maybe not perfect. Twilight did live in the Library - making it look like something awful happened to her home might be a bit too much for her to take. Just the books, then. Something with the books. What could she do with the books...
Re-arranging them wouldn't do any good. Twilight did that all the time - and even if she didn't, "moving books into different places" did not make for a very good story. She couldn't brag about that later to anybody. Also, too much work. Maybe she could make it look like something had happened to the books. Like, they got damaged. Rainbow Dash remembered the lecture she'd gotten just for returning a Daring Do book she'd bent a page on.
Rainbow Dash rolled her eyes at the memory. She'd misplaced her bookmark - what was she supposed to do?
Back to the prank. She could have made it look like the books had all been stolen - but that was as much work as rearranging them and then some, because Twilight would probably make her put them all back. She couldn't make it look like all the pages had been bent without actually doing it - a lot of work still. If there was just something she could quickly do to all of them at once.
Like painting them.
She'd had to go ask Rarity about paints. She needed something that could come off easy without damaging what it was on. Rarity had oohed and aahed over different supplies till she produced something worthwhile - a type of paint that was enchanted to peel off easily. Rarity had also explained that a unicorn could just levitate it off and put it back into the bucket if they wanted to. It was perfect.
So Rainbow got a tub full of the magic paint in black. She had then suggested to Twilight that maybe Applejack's cider could be improved if her cellar was, oh, say, 20 percent cooler. Twilight had made a face as she thought about it, then gone to do some tests. While she was out, Rainbow took the magic paint and slathered the books in it. She tried to make it look like they'd been burned, but focused more on covering as much of them as possible. The goal was shock more than tedious exposition, after all.
After that, all she had to do was wait. And wait she did. Rainbow Dash began to wonder if perhaps she had chosen too complex a diversion for Twilght - how many tests would she run before Applejack told her to go home?
Quite a few, as it turned out. Twilight came back loaded down with papers and a few apple pies just as it started to get dark. She moved the pies to her kitchen before going over her data sheets, levitating them in the air and squinting at them. Rainbow Dash shifted her weight and tried to stay as quiet as possible. Any second now...
Twilight blinked and looked at a bookshelf. She blinked more, and turned to look at another. And another, and another. Rainbow Dash supressed a giggle - she couldn't see Twilight's face now that she had turned her head, but she could just imagine her pinprick eyes, her gaping mouth, the inevitable scream -
"Sigh."
That was not what she was expecting. It was Rainbow Dash's turn to blink as Twilight hung her head slightly and neatly stacked up her pile of papers. She then calmly -calmly- walked over to a shelf and pulled a book off with her hooves. She opened it, flipped through a few pages before she sighed again and put it back.
"Well, that's unpleasant."
"UNPLEASANT!?" Rainbow Dash shrieked. That, at least, caused Twilight to flinch slightly. She flew out from her hiding spot and pressed herself face to face with Twilight. "You come home to see all your books vandalized, and the word Miss Egghead Princess uses is UNPLEASANT?"
Twilight cleared her throat. "It is a very accurate word to describe the situation - "
Rainbow facehooved. "I spent forever planning this prank, and it was perfect. But of course you were able to tell that the paint was magic - "
"Oh, it is?"
Rainbow stared at her for a moment. "...you didn't know it was magic."
"What kind of magic is it? Is it glow in the dark?"
"You didn't realize that the paint would come right off, and you didn't freak out."
"Ohhh Rarity mentioned these paints once before, very useful for budding artists who want to get a good sketch done but are short on supplies -"
Rainbow Dash grabbed Twilights face, squishing her cheeks and silencing the purple pony princess. "You mean to tell me that for all you knew, your books were ruined. Ruined. At best, vandalized and at worst destroyed, and you called it 'unpleasant'"
Twilight frowned as best she could with her cheeks smushed together. She muttered through forcibly pursed lips "I don't see what you have against the word - "
Rainbow threw her hooves back in the air. "That's not the point! You're Twilight Sparkle! You go friggen nuts when the littlest thing goes wrong - you worked yourself to death over the Pinkie Sense, you turned the town into zombies because of a late letter!"
Twilight blushed slightly. "Those weren't my best moments, I admit, but I've changed since then."
Rainbow Dash narrowed her eyes and crossed her hooves. "You're right, you have changed. What really happened, the day you got those wings, Twi?"
Twilight started to sweat. "I don't know what you are talking about. We all know what happened - I fixed Star Swirl the Bearded's spell, and it sent me to a Celestial Plane where - "
"Is that how it happened?" Rainbow Dash dropped down on all fours and started advancing. "Because I remember you getting shot up with magic lasers after completely botching a spell, disappearing, then suddenly showing back up with wings. You haven't been the same since. What. Happened?"
Twilight continued backing up till her rump bumped a bookcase. "I - I just told you. Please stop asking questions."
"Then give me some answers, Twilight! If that is even your real name!" Rainbow dash punctuated the last remark with her eyeballs.
Twilight looked from left to right, frantically for a normal pony but nowhere near Twilight levels of frantic before she sighed.
"I guess it was only a matter of time..."
She erupted into green flames. Rainbow was knocked onto her back from the eruption of pure power.
Where the Perfect Purple Pony Princess once stood now stood a Changeling. A large one, much like Chrysalis, but more blue than green. Rainbow gaped as the changeling cackled.
"Who...who are you?"
A fanged grin was the first response. "Oh, nopony special. You won't remember any of this, why bother asking?"
Rainbow swallowed nervously. "Uhm, well, if I won't remember, why not tell?"
The changling chuckled. "Fair enough. I am the ruler of a faraway land. As important as Twilight was to you, she was also to us. Our very survival hinged on how she was received, how she was seen by others. We couldn't have a regular student with anxiety problems leading the charge for us, oh no. So we arranged to have her replaced by a calm, collected, perfect princess. Just like Cadence."
Rainbow gulped. "Are...are you in league with Chrysalis?"
"Not as such, no." The changeling lit her horn and angled it towards Rainbow's forehead. "But I've spent enough time dawdling here with you. My name...my name is Hasbro."
Rainbow saw only the blue glow.
She blinked. Why was she in the library? Why were all the books covered in black goo?
"Twilight? What's going on?"
Princess Twilight chuckled as she pulled the blackness off of a book. "Nothing important. Just a little experiment mishap, I'll have it cleaned up in a jiffy. You should probably head home though, it's getting late."
Rainbow looked outside - it was, in fact, very dark. The stars were out already. "Sheesh, sorry Twilight. Good luck with your ah...stuff."
The Pegasus drifted hazily towards the door. Why was she so dizzy? And what were these odd thoughts in her head?
Well, it couldn't hurt to share them with Twilight before she left.
"Hey, I just had a funny thought."
Twilight paused a little longer than she should have before responding. "Oh? What's that."
Rainbow grinned. "You - I mean us, like all us friends - we should have more rainbows and stuff going on, ya dig?"
Twilight grinned back. "I like the way you think."