A guest takes a visit to Equestria.

"Breaking news! A large potato is destroying Ponyville!" Said the newspony, on channel 69 on the TV Twilight Sparkle owned. Spike was watching in amazement at the TV while Twilight had a war helmet on and a pillow to defend her home with.

"What happened to the guest, Twilight? You don't think he had something to do with this, do you?" Spike said, worriedly.

"I don't know, but we need to find him if we're going to-" Twilight said, being interrupted as she saw a note that the guest puked out. She read it, and now she knew where to go. "Spike, get your stuff in a backpack. We're going to Sugar Cube corner." Twilight said, with a depth of field effect behind her.

"Aaaah! Why is everything so darn blurry?!" Her assistant said.

Five minutes earlier.....

Guest 8543 was feeling like he needed to excrete his glorious waste, because it now came to the point that he needed to after consuming the liquid. He then went outside, and then shat some neon green blocks that had a glowing effect. He then walked away as the ponies that where around him stared in confusion. Then they looked at the green blocks he excreted.

"Woah, what is that?" Said one pony.

There where a lot of murmurs, and then some homeless guy just trotted up and ate it.

"Hmm, tastes like shit!" the homeless pony said, before mutating into a huge potato. The potato then grew legs that looked muscly and then stood up. There where gasps of confusion.

The potato was twice the height of Sugar Cube Corner. It then grew arms that had bulging biceps, and proceeded to tear some buildings up. It was pandemonium! Every single one of the townsfolk that was near the homeless pony that ate the radioactive shit was running around helplessly!

Gee, if only SOMEONE would help!

The Doctor and Lyra got out of the TARDIS after Lyra got some info about him. But nothing too personal.

"Uh, Doctor? Why is there a potato destroying the town?" Lyra asked.

"Oh, don't be silly. That isn't possible-" The Doctor said before turning around and seeing the potato. "Oh, I love impossible things!" He said, running towards it with his sonic screwdriver in his hand. Lyra was confused.

"Come on, let's go near danger!" the Doctor said, Lyra following behind, grinning.

The Doctor finally got to near where the potato was and started scanning it with his screwdriver. "Lyra, I need you to get as many people in cover as fast as you can, I'm going to find a way to stop this thing from destroying your nice little town!" He said. Ducking from a broken pipe that nearly hit him in the face, and getting lodged into a wall.

"Alright!" Lyra said as she ran to do what the Doctor said.

"Okay, let's see what you are..." the Doctor said, looking at his screwdriver. "It has pony DNA, along with.... LUA radioactivity? Some traces of chocolate milk, and..... oh my." the Doctor said to no one in particular.

There's a ROBLOXian here in Ponyville? the Doctor thought. I need to find it and bring it home, poor creature's probably scared. It's been a while since the Doctor had seen a ROBLOXian, maybe it's been, like, 500 years or so, but he saw them when they first learned to build. Then there came these "Guests" that ranged usually from a number 1 to 20,000. Thankfully there where only 20,000 out of the 5 million ROBLOXians.

The Doctor knew how to defeat the potato monster.

Twilight was running towards the potato, looking for the guest. She was then stopped by the Doctor. "You there... Twilight Sparkle, am I right? Get over here! Something might crash into you!" He said.

Twilight obeyed and crouched down beside him, just in time, too. Where she once was, a building collapsed and fell over due to the potato that was trying to destroy everything.

Lyra got back to the Doctor because she got as many ponies out of trouble from the potato as she could and she was tired. Oh, how she would like to have a milkshake right now.

"Doctor, I'm back! And hey, Twilight!" Lyra said.

"Right now I don't think it's time to celebrate you two seeing each other, there's a giant potato that's going to kill us all if we don't stop it." The Doctor said, breaking out into laughter. "Oooh, couldn't keep a straight face. It's mad, I tell you!"

"Well, how are we going to stop it?" Twilight asked.

"We need to find the ROBLOXian. Only he or she has the power to delete that potato." He said.

"Oh, you know about them? I was keeping one in my library... I think I'm friends with it!" Twilight said.

"Really? Well, that's convenient." The Doctor said.

"How'd you miss it? It was in her library while Pinkie was hosting that rockin' awesome party!" Lyra said.

"It was in there?!" The Doctor said, facepalming. He didn't know how he could miss something so potentially dangerous.

"What's the ROBLOXian's name?" He asked. "Did you even manage to get the name?"

"Yes, he said it was Guest 8543." Twilight replied.

The Doctor gasped. "A guest? In this town?"

Twilight nodded.

"Oh my. This might be harder than I tho-" He said, being cut off by the guest walking in front of him.

"HIYO!" yelled the guest.

"Hello, would you mind deleting the walking potato that going to kill you all?" the Doctor said.

"I like potatoes." Guest 8543 said, being hit in the head by some debris. The guest, however, wasn't harmed at all.

"That's nice, but the potato might be superior to you if you don't kill it." the Doctor said. He knew that all guests thought highly of themselves, and that they thought they where the boss. Guests will destroy anything that ticks them off if you weren't careful.

"NOTHING IS SUPERIOR TO MEEEE, GET TEH EPIC DUCKS!" the guest said, pulling out a rubber ducky out of nowhere and started to chase after the monster potato.