The transformation overwhelms Fluttershy in seconds, making her lose balance and drop Applejack from her arms. The former farmer girl falls on her back and flinches a bit, and Fluttershy collapses on her knees, as her body is transformed in seconds. Her ears keep sprouting a membrane and rays until they are fully formed earfins, her gills develop fast under the latter and she gasps for air. She can breath but with certain difficulty, however she does not notice that as her feet explosively grow and morph into fins with thick fish rays, which fuse in seconds into a tailfin. Her leg bones crumble away as the legs fuse and her spine fills in the void, forming her tail. Thousands of scales break free off her soft skin. In seconds, the transformation is over and Fluttershy is still on the kneeled position behind Applejack, who has already managed to contact Sunset Shimmer on the phone and is now on the Speaker.
 
Sunset Shimmer: Hi Applejack! I am sorry I couldn’t answer earlier. I saw you tried to call earlier but you didn’t leave a message… what’s up?  
Applejack: Sunset! Thank God you answered! Where are you? We need your help urgently! We are knee-deep in trouble around here! We got us in a Texas Sized Pickle of a problem here. Sumthin’ is turning us all into mermaids!!!  
Sunset Shimmer: Mermaids? Come on Applejack… Are you just kidding with me like Pinkie Pie just did?  
Applejack: What in tarnat….? How…? How did Pinkie contact you?  
Sunset Shimmer: Pinkie Pie just sent me a message and told me exactly the same thing. That she was turned into a mermaid along with all the other girls, at the pier by the sea. And that I should go there too, she told me I could know everything that happened to them… if I touched her or any of the girls, you know, by reading their minds as usual… I thought it was just a prank because of the cosplaying contest that is being held at the beach.  
Applejack: Okay…. I don’t want to know how Pinkie did that. * darn * It is true, Sunset. We are all being turned into mermaids  
Sunset Shimmer: What? How?  
Applejack: It all started when Princess Twilight Sparkle returned here…  
Sunset Shimmer: Wait… Twilight? Our Twilight has come back to this world?  
Applejack: Yeah. She did, and she kinda brought a curse with her… that is turning us all into fish people.  
Sunset: Okay, I believe you. I need to see that. We ought to meet somewhere and go to the bottom of the issue. Where are you now?  
Applejack: Right now I came back to the rented house near Bonampak Avenue, I am here with Fluttershy. I managed to get by on land by driving Pinkie’s scooter. But Ah’m afraid that she got also the Mermaid Flu.  
Sunset: Oh my… Let’s do something… Let’s have a rendezvous at the store near the Hotel Zone by the beach, at the entrance of the pier, do you think you can…. wait… did you say Pinkie’s Scooter and that Fluttershy got the Mermadi Flu?  
Applejack: So to say…. Yes, she transformed too.  
Sunset: Pinkie just sent me another text message, she says that somebody stole her scooter. She knows because Scootaloo texted her… saying that she filled a Grand Theft report of the scooter…
 
Suddenly, the blaring sirens of a police cruiser are heard in the distance. Applejack lets the phone fall from her hand. She and Flutterhsy panic as the siren gets louder.
 
We gotta get out of here!!!!

@Patometro06  
I hope this comment did not make you uncomfortable. That was never the intent.

@Background Pony #70A9  
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Ponies’ll love this. The most attractive versions of these two any of us will see. Tails are so much nicer than legs. I fantasized about it. And wish myself in their position if only for a day.
 
Mermaids in dresses is always fine, too. And Fluttershy has a green tail. All the others have one that matches something of theirs, like their hair or their coats.