Author's Note

These chapters probably all take place at different times. This one is the day after the mirror pool incident in "Too Many Pinkie Pies".

The Mirror Pool

Pinkie Pie waved. "Hi, Twilight! What brings you into Sugarcube Corner today? You want a cupcake? I just whipped up a fresh batch!"

"Well, actually, I wanted to talk. But a cupcake sounds nice too."

Pinkie Pie handed her a cupcake swirled with brown and yellow, with bright orange frosting. "Chocolate orange swirl!" she said proudly. "Two bits, because Mrs Cake says I'm not allowed to give my friends free cupcakes anymore."

"Pinkie, everypony in town is your friend," Twilight said as she passed over two coins. "And you can't give everypony free cupcakes, or Sugarcube corner will go bankrupt."

"No way! That's exactly what Mrs Cake said!" Pinkie reached past Twilight, extending her leg much farther than it had any right to extend, and pulled up a chair. "So, tell me, what's up? What's bothering you?"

"Well..." Twilight sighed. "It's the mirror pool. All those Pinkies that came out of it... did we kill them?"

"Of course not, silly! You just sent them back into it! You even said so!"

"I know that's what the spell said, but what does that mean? If you created life by bringing them out, doesn't that mean I ended that life by returning them?"

Pinkie shook her head. "No, Twilight, it doesn't work that way. It's more like..." She paused, searching for the right metaphor. "It's like a row of houses! Only, in each house is the exact same family."

"Wait, what?"

"Imagine me and my family lived on a big street, and in each house on the street there was another version of my family. I could go to another house and knock on their door, and ask their Pinkie to come over and play at my house, see? Only the metaphor isn't perfect, because when they come to visit at my house then they forget a lot about who they are, and they only remember the thing that made me go over and invite them. Like yesterday, when I went to the mirror pool, I just wanted to have fun. So fun was the only thing all the Pinkies could think about. And then when you sent them back, it was like if my mom told all the Pinkies that they'd spent long enough at my house and it was time for them to go back home. Then when they go back home, more of who they really are comes back! You see?"

"Wait, you're saying... the mirror pool connects to other universes? And they're all exactly the same?"

"That's right! I knew you'd understand!" She patted Twilight on the head.

"But... but... how many are there?"

"As many as there need to be, silly!" Pinkie giggled.

Twilight's mouth dropped. "An infinite number of identical universes? How come nopony knows about this?"

"Don't be silly, Twilight! I know about it! And you haven't eaten your cupcake."

Thrown off by this abrupt subject change, Twilight glanced down. "Oh, you're right. But why are you the only one who knows about this?" She took a bite. "Wow, that's delicious!"

"I know! And the mirror pool is an old family story. I guess somepony way back in my family tree found it while mining one day."

"But- but- Pinkie, this is huge! An infinite multiverse and a single point at which they overlap! This could be a big discovery!"

Pinkie scoffed. "Yeah, and really dangerous! Twilight, listen to me. This is actually serious." She leaned forwards until her muzzle was inches from Twilight's. "Do you know why that book specifically warned you to be sure you didn't send the real me back into the mirror pool?"

Twilight shook her head, backing away from Pinkie's uncomfortable closeness.

"Let's go back to the houses. If you kick the neighbors out of your house, they'll just go back to your own. But if you kicked me out of my own house, I'd have nowhere to go! I'd be wandering the street forever. And because of the mirror pool's magic, I wouldn't be able to come back, and I wouldn't be able to go into anypony else's house either. I'd be stuck! Forever!"

Twilight paled.

"If you tell everyone about this, everypony will want to go to the mirror pool! Dozens of them will come in here, or else they'll go to other places. You and all the other yous will make mistakes and send back the wrong ponies, at least sometimes! And then there'll be ponies wandering around inside the pool, lost for all of time!"

Twilight swallowed hard. "Okay, Pinkie. I'll leave the pool alone."

"Good, 'cause I hadn't even started to get into the consequences if a badguy found the pool!" She leaned in close and whispered, "Between you and me, I think the FlimFlam brothers might actually be mirror clones, and then one changed his name, grew a mustache, and disguised his cutie mark so it wasn't so obvious."

"That's an... interesting theory... but I'm pretty sure they're just twins, Pinkie."

She shrugged. "Eh, you're entitled to your own opinion. But it's a conspiracy, I'm telling you." She glanced down at the rest of Twilight's cupcake. "You gonna eat that?"

"Oh- yes. I guess I wasn't paying much attention to that while we talked." Twilight picked it up. "Well, thanks for explaining the pool, Pinkie. You've given me a lot to think about."