As Pinkie Pie folded the letter back up, she noticed some writing on the back.
"P.S. To help solve this friendship problem, why not talk it out with Twilight?"
Pinkie said, "Of course!"
She put on a fake mustache (for safety, just in case) and took a walk to the Ponyville Library. She knocked on the door. "Hello?" she said.
A moment later the door opened. "Hi, Pinkie!" Twilight Sparkle said with a smile. "I like the new 'do!"
Behind Twilight, Spike groaned. "Oh, sure!" he complained, "When SHE grows a mustache you like it. But when I want just a little bit of magical help growing my own, you put your hoof down."
Pinkie Pie said, "The mustache is just a fake, silly! But that's what I'm here to talk to Twilight about."
Twilight seemed puzzled. "You want to talk about a fake mustache?"
Pinkie said, "Not just the mustache. The DEEP dark truths BEHIND the mustache." Then she whispered, "Is there a place where we can talk privately, so nopony will hear us?"
Twilight beckoned Pinkie into the library, and lit up her horn to cast a magenta bubble of soundproofing around the two ponies.
"There!" Twilight said in an oddly echoing tone, "Privacy!"
Pinkie said cheerfully, "And because I saw you cast that spell, now I can be extra-sure that you're really you! And not just somepony who looks like you!"
Twilight frowned. "Pinkie, please tell me about those deep, dark truths you mentioned."
"Well," Pinkie said, "Remember the time that I used the Mirror Pool to make copies of myself, and it got all confusing?"
Twilight gasped. "Oh no! Did it happen again? What will we do? I HATE vaporizing ponies who look exactly like my friends!"
She looked around nervously. "Where are they? Have they taken over Ponyville? Are you the real you, or are you one of the copies?" Twilight started hyperventilating.
Pinkie reached into her poofy mane and pulled out a paper bag, which she hoofed to Twilight. Twilight held the bag up and breathed into it.
After a moment, Twilight smiled. "See, I'm fine! Even if Ponyville is being infiltrated by an army of shapeshifters, I can cope!" Pinkie thought the unicorn's smile looked a little forced.
"No," Pinkie Pie said, "There isn't any army of shapeshifters infiltrating Ponyville that I know of. But ever since you vaporized dozens of ponyclones who looked exactly like me, I've been having nightmares. So I thought in case anything like that happens again, we should prepare in advance."
Twilight blinked. "You thought we should prepare in advance? Just in case of an invasion of copyponies who look exactly like us?"
"Yes!" Pinkie said.
Twilight looked nervous. "Who are you and what did you do with the real happy-go-lucky Pinkie Pie?"
Pinkie stomped her hoof. "Now look here! Just because I'm a fun party pony, doesn't mean that I don't have feelings! YOU said YOU hate vaporising ponies who look exactly like your friends! And I hate being threatened with being vaporized just because somepony...somemonster...whoever, looks exactly like me.
"I AM Ponyville's premier party planner. But you don't get to be a premier party planner by NOT planning ahead and NOT preparing! So listen to me, and let's plan ahead and prepare, just in case!"
Twilight blinked. "That seems very...reasonable."
Twilight's horn flared a few times. "Sorry," she said, "Just checking that you're not a changeling...and for a few other things."
Pinkie nodded. "That's okey-dokey," she said. "So...I'm not those things, right?"
Twilight giggled. "Seems to me, you're just our lovable Pinkie Pie."
"Phew!" Pinkie said, "That's what I thought! But it IS best to make sure. So anyway, about this planning...I've never planned a Got To Make Sure That You're Really Pinkie Pie And Not Some Evil Monster Party. Do you have any ideas?"
"When I was a little filly, Cadance taught me a poem, and a dance that goes with it. When she didn't know it years later, that was a clue something was wrong. A changeling had secretly replaced her," Twilight said. She started chanting and doing a little dance. "Sunshine, sunshine! Ladybugs awake! Clap your hooves, and do a little shake!"
Pinkie stared at Twilight. "It's really amazing, when you think about it," she said.
Twilight stared back at her. "What?"
"It's a good thing I've seen you do that before, and I saw you do it just fine last time too. Because except for that one little song-and-dance, you're usually the worst dancer in Equestria."
"Okay," Twilight said. "Do you think anypony else COULD dance as badly as I do?"
Pinkie stroked her mane as she thought. "What I said wasn't quite right. I've seen you line dance kind of okay. But when you dance by yourself...well..."
"Well what?"
"Well I'm always happy to know my friend Twilight is having fun."
"This isn't the time for tact, Pinkie! I need honesty here. Can anypony else dance as badly as me? Can anycreature? Be honest!"
Pinkie shook her head. "I refuse to say."
"So I am recognizably THE WORST DANCER IN ALL EQUESTRIA? And maybe beyond?"
Pinkie cried. "I am so sorry. I didn't mean to insult you and make you feel bad."
"Honesty!" Twilight snorted. "Where is Applejack when we need her? Maybe we should go get her. Or you can tell me the truth yourself."
Pinkie bawled. "Yes, Twilight! As a solo act, you are the worst dancer in Equestria! I am SO SORRY!"
"Well, then!" Twilight said in a satisified way, "No problem."
"No problem? I insulted you and--"
"I'm happy! Really I am!"
"Happy?"
"Pinkie, if you ever suspect that I've been replaced, by a changeling, or a Mirror Pool clone, or by some horrible creature that we haven't even heard of yet...all you have to do is pull out a musical instrument or a record player, and..."
"Now I see!" Pinkie said joyfully, tears still running down her face. "I just play some music and ask you to dance..."
"And make me the happiest pony in the world!" Twilight hugged her friend.
"What?" Pinkie said.
"Oh," Twilight said, "I mean...I'm so happy to have such a good friend who cares enough to check that it's really me and save me from getting blown up by a giant cannon or something."
"Yes," Pinkie said. "About that...I might have written a few letters to Celestia recently..."
***
After Pinkie explained, Twilight said, "Oh! That's okay! Because now we have a pretty good plan to keep me from getting blown up. We can even tell Celestia and Luna and the Royal Guard. If anypony ever suspects that I'm not really me, all they have to do is start playing some dance music and ask me to prove my identity. Maybe they can even put up some party streamers and balloons to help provide the right atmosphere."
Pinkie laughed. "So we've planned a Save Twilight Or Expose the Twilight Impostor If Everypony Gets Confused About Who's Who Party."
Twilight hugged Pinkie. "You really are the best party planner ever."
Twilight and Pinkie went to Sugarcube Corner to celebrate by eating cupcakes and drinking tea. When they got back to the library, Twilight wrote a letter describing the plan and sent it to Celestia.
Pinkie was so happy that she'd discovered a way to protect Equestria's newest princess from impersonation plots.
It was only that night, laying in bed, that Pinkie Pie remembered her fears. She said to herself, "When I visited Twilight today, why did I get distracted from the reason I went to see her?
"It's like I couldn't concentrate on one thing even to save my own life!"
So Pinkie got up, opened a can of paint, and practiced her concentration exercises again.