The Doctor had trouble getting there as well, his new wings were tempted to fly, and he couldn't seem to control them. "Blast! I want my hooves on the ground, you idiotic wings!"
"Hey, my wings aren't id-id...stupid!" Derpy protested.
Bon Bon looked over at them, then seemed to whisper to Lyra, "Gee, I thought all pegasus knew how to fly." they both snickered.
They both just ignored them, and kept carrying on to Twilight's castle. Finally, Derpy and Doctor had reached it. "Quickly, knock on the door! I can't see straight, or fly straight for that matter!" the Doctor exclaimed.
Derpy swiftly ran over and knocked on her door. "Princess Twilight, we need your help! Doc's machine wasn't working and, and..."
"Whoa, hold up, aren't you talking about yourself?" Twilight answered, looking surprised when opening the door.
"No, no! Our bodies are mixed up! You gotta help us!" Derpy pleaded.
Twilight looked back at Doctor, who still had trouble making his way to the door. "I see. I can also tell, because most pegasus can fly at this age."
He finally made his way over to explain, "Princess, our bodies have been switched, you need to aid us. I have a science fair to attend momentarily! You must fix my contraption!"
"B-But I don't know the first thing about machinery!" Twilight protested.
Derpy recalled, "But you made the portal in The Crystal Empire work again! You made that device to power the portal! Surely you could try to fix his machine!"
"Wait a second, how did you know about the portal? No pony is supposed to know about that!" Twilight shouted.
The Doctor stated, "Well. You certainly aren't doing a good job keeping your muzzle shut about 'it'." his wings began taking off again, but he managed to stay down to Earth.
"Princess Twilight, please, you need to help us. Doc has to win that competition!" Derpy pleaded once more.
The alicorn exhaled and replied, "I will try, but I can't promise anything. Alright?"
"Fair enough, your majesty." the Doctor said. So he didn't have to struggle again, Twilight used her magic to teleport them to his lab. "Ugh...I hate traveling by magic..."
"Do you or do you not want my assistance?" Twilight questioned.
He rolled his eyes, "Just come on, I want to get out of here!"
"Ahem." Derpy coughed.
Doctor chuckled nervously, "No offense, Derpy."
"None taken..." she responded coldly. On the inside, she didn't take it too hard.
Twilight used her magic to levitate a few tools. She listened as Doctor Whooves instructed her where to fix it. The machine had burst after being used, but it was being made stronger with every screw she tightened.
"And you just need to tighten up the last washer over there." Dr. Whooves finished off.
Twilight asked, "Okay, now what?"
"Pull the lever." he remarked. Twilight put a force-field around her to be sure she didn't hit herself, and then she pulled the lever. In almost an instant, Derpy and the Doctor's bodies were in the right place again. "Thank you, Twilight! Now, there's no time to waste...and I should know. We have to get to the science fair, now!"
"Not a problem." Twilight teleported them there, along with the machine in an open spot of the fair. "I'm also one of the judges, and you sure have my vote on this contraption!"
"Thank you, your highness! I hope I win, but if not, that's fine. For now, I think it's a better idea for you to enjoy the rest of the fair. I hear somepony brought radioactive animals." Dr. Whooves stated.
Derpy was confused, "...Somepony could really do that?"
"I don't see why it wouldn't be possible, but even so, it's just a rumor." the Doctor replied.
Princess Cadance was one of the judges, and as she walked by, the device caught her eye. "Hmm. Your invention seems very interesting, Doc. What exactly does it do?"
"This machine can switch anypony's bodies in the blink of an eye. Believe me, I've tested it. Derpy here was my...uh...'assistant'." Doctor Whooves shakily said.
"Hmm...well, you've got my vote! Good luck winning the fair!" Princess Cadance smiled and checked her board, then walked away to another project.
Not long after, Princess Celestia was up on stage at the front of the fair, "Everypony, the time has come to announce the winner of this year's Ponyville Science Fair! Now, even though you may not have been the one to win, just know that we've all seen some pretty fascinating inventions and it was a tough choice. However, we can only have one winner here, and the Inventor's Trophy goes to...Dr. Whooves!" cheers roared over a crowd of inventors, and many ponies congratulated Dr. Whooves.
"Wow! You won, Doc! Congratulations!" Derpy smiled.
"Thank you, Derpy. Even though you sort of messed with my machine, I don't think I could have won this without you." he remarked. He gave her the trophy instead. Derpy smiled once more, and then after the fair, they both went home and were ready to start another day.