Alternate Culprit 1:
The following takes place after Rarity admits to wearing falsies. No other suspects were called.
"Care to explain yourself?" asked Twilight.
Rarity sighs and begins.
"It was the middle of the night, I was asleep in my room when I heard hoofsteps in the hallway. I woke up and looked outside to find that Applejack was sneaking around. I followed her into the dessert car. After she hid, I was caught by Pinkie Pie and accused as a saboteur and ran back to my room. Luckily, I was fast enough. When she went to the engine, I went back to the dessert car to stop Applejack from doing anything...But it was too late! Two bites were taken out of the cake! When Pinkie came back, I hid. I tried saving the rest of the cake by darkening out the car, but to my surprise, Applejack took advantage of this and struck again. I chased her back to the rooms and lost my eyelash on the portrait"
"That's very interesting" said Twilight, "Especially since when Applejack said she couldn't wait to taste the entries at the competition"
Everypony turns over to Applejack who sighs.
"Fine, I admit it" she said. "But can y'all blame me? Pinkie made everything sound so irresistable, I just couldn't help myself, so I did. I'm a 'might sorry, everypony"
That's one way that could've went down, but consider this next one.
Alternate Culprit 2:
The following takes place after Twilight takes the feather out of the envelope. The feather is gray rather then blue. The cowd gasps.
"A-ha!" Shouted Pinkie Pie, "A gray feather. I knew it was you, Gustave le Grand!"
"Pinkie, this feather is too grey to be Gustave's. Remember how when you chased the suspect to the caboose, they suddenly disappeared? That's because they FLEW away. But the thief left this feather behind, possibly a tenth passenger"
"Hmm, you might be onto something"
"And when we went to the engine, I saw the conductor's hat. And inside the hat was... this" Twilight finished pulling a strand of yellow hair out of the enelope.
Pinkie rushes to Rainbow Dash saying "So it WAS you, that yellow hair came from your rainbow colored mane!"
"It's too long to have come from MY mane!"
"Pinkie, remember? You chased a pony to the engine, where you thought you saw the conductor shoveling coal, but that wasn't the conductor at all. It was either Applejack or, the tenth passenger"
The crowd gasps again.
"I'm innocent, I was in my room all night!"
"But then another clue confounded my suspicions. You were guarding the cake when the curtains mysteriously closed. But that's no mystery, that's magic. But when the thief tried to make their great escape, they left a little addition to the portrait. Has anypony else noticed that Rarity is wearing her hair rather differently today?"
Rarity gasps.
"What? Is it a crime to change one's style every now and again? Why, I think it's a crime not to"
"Really?" asked Twilight removing the hair from Rarity's lashless eye.
"FINE, I'M GUILTY!" cried the distraught unicorn, "I WEAR FALSE EYELASHES!"
"Continue" said Twilight.
"I woke up to the commotion Pinkie was making. I was too tired to see, but there was a third pony in the car with us. So I closed the curtains to stop them. Unfortunately, to no avail. The theif knocked me into the portrait and that's where I lost my eyelash"
"Then I don't get it" said Fluttershy, "Who's been eating all the desserts?"
As Twilight was about to answer, who should walk into the dessert car about to take a bite out of the Mousse Moose's antler but...
"DERPY!"
"Hi, guys!"
"Why have you been the entries for the national dessert competition?"
"...You mean this isn't the DINING car?"
Twilight sighs at this while the others groaned.
"Oh my"
Huh? Huh? Didn't expect THAT one, did you? Well, we've got one more.
Alternate Culprits 3-5:
The following takes place just before Twilight reveals the evidence.
"Just a sec there, Twi" said AJ.
"What?"
"Just wanted to say 'fore you revealed that evidence, I've already solved this mystery!"
Everypony gasps.
"Y'see" AJ continued, "While Big Mac was fixin' the car to fit the cake in, I heard hoofsteps made by three little fillies. Last night, I wanted to investigate while everypony else was asleep. With Rainbow and Rarity's help, I tried to make sure I found who was in the car, but Pinkie was on full alert and we all got scattered. I wound up in the engin room and had to act fast while she was chasin' Rainbow Dash. I disguised myself as the conductor to save the secrecy of my mission. Rarity closed the curtains in order to sneek me to the otherside of the car, but that just riled her up. I continued my investigation while you asked us to got to our-"
"I CAN'T TAKE IT ANY MORE!" cried Sweetie Belle opping out from under MMMM's table.
"Sweetie Belle!? How could you?"
"It wasn't just me!"
Apple Bloom and Scootaloo come out.
"We were so curious about the cake, so we followed you" admitted Apple Bloom. "We tried to get out after Big Mac fixed the car, but everypony keept comin' in!"
"Then Pinkie started about how everyting was SO good" added Scootaloo.
"We couldn't help ourselves" said Sweetie Belle.
"We're sorry, everypony" all three said.
Everypony simply laughed.
