Author's Note: Last one tonight, I promise! This is a short, humorous Pokémon (Mystery Dungeon, I guess,) and Doctor Who crossover.

The Doctor finished his ten minute rapid fire speech and threw his arms wide in excitement. “Ta-dah!”
Amy and Rory just stared at him.
“Wait,” Rory said blankly, “Say that again?”
The Doctor sighed at the slowness of his companions and gestured again at the strange piece of headgear hanging down in the TARDIS. “A Kecleon Arch!” he repeated energetically, “It’s a variation on the Chameleon Arch I once used to transform myself into a human! And it could turn us into any one of the creatures in the devices I’ve given you by…” then, noticing the expressions of the others, “Well… It has to do with Ditto’s ‘transform’ move. Which is odd, because it’s a Kecleon Arch. Isn’t that odd? I think it’s odd. Anyway, yes. Turns you into a Pokémon. Which one you become is based upon traits you already hold inside you. Should be great fun, and only slightly excruciatingly painful, and then we’ll get to explore the Pokémon world! Should be amazing; I’ve heard Treasure Town is really nice.”
“We’re going to be… one of these?” Rory said doubtfully as he clicked through the entries in the device the Doctor had handed him to look at. He’d called it a pokédex.
“Yes Rory,” the Doctor replied, “Although if you keep acting like this it will probably make you something useless like a Caterpie and then we’ll never get anywhere.”
Amy laughed, and shoved her husband playfully. “Yeah Rory! Don’t drag us down by turning into a bug!”
“Yeah, whatever,” Rory replied, frowning at the Doctor, “Are you sure this is in any way safe? Have you even tried it out before?”
“Nope! Never used it before in my life!” the Doctor cried cheerfully, “Can’t wait to find out which Pokémon I am! It’s long been a dream of mine, but even with the TARDIS sometimes you just don’t get the time! You know, universe always getting itself in peril and all…”
“Well isn’t anywhere in peril now?” Amy asked sensibly.
“Yes in fact,” the Doctor explained, “But it just so happens to be the Pokémon world. Time has been disrupted and the time gears are going missing. But we’ll look into all of that when we get there! Come on!”
“Okay,” Amy agreed, “I’m in. Can I use the arch first?”
“I don’t see why not,” the Doctor assented, “It’s pretty stable technology. I wonder which Pokémon you’ll be…?”
She grinned, and put on the Kecleon Arch. “Let’s find out.”
“I wonder… Her name is Pond… Will she be a water Pokémon?” the Doctor continued to muse as Amy let out a small shriek of pain behind him when her body began to change.
“Hey, Doctor,” Rory cut him off, indicating towards his wife.
“OH!” he exclaimed upon turning around.
Amy had taken the form of a small, glossy furred and reddish-orange fox-like creature with several large, fluffy tails.
“A Vulpix!” the Doctor shouted excitedly, “Brilliant! I think I see where that came from… Ginger and all…”
“Not to mention her fiery personality,” Rory pointed out, and then he bent down to look at her. “Hey, Amy. Are you alright?”
“Vulpix, vul!” Amy replied in a small, high-pitched voice.
“Oh yes,” the Doctor said to Rory, “I’d forgotten to mention… Pokémon can only say their names. Humans can’t understand them. I however, can. She says she’s fine. She wants you to go next.”
Rory hesitated, and then nodded determinedly. “Okay, I’m ready.”
“I wouldn’t hold out too much hope though, Rory,” the Doctor put in, “There are an awful lot of Pokémon in the world. The chances of you turning out to be anything as decent as a Vulpix like Amy are very slim.”
“Gee, thanks Doctor,” Rory said sarcastically as he picked up the Kecleon Arch.
“You could be an Unown which can only learn hidden power, or even a Weedle!” The Doctor continued, wincing, “Or a Combee! Or a Pichu! How would we save them if you were one of those?”
Rory shrugged and put on the Kecleon Arch. “Like Amy said, there’s only one way to find out!”
A quick scream of pain later and the Doctor let out a shocked gasp.
“VULPIX!” Amy cried in impressed surprise.
“I know!” the Doctor agreed, “Where did that come from?!”
Rory was a huge, awesome-looking Dragonite. Grinning, he whipped out his blue wings experimentally and turned in a circle as if trying to see his tail. (Which he totally was.)
“Maybe it’s because he’s loyal and brave,” Amy suggested, staring up at him in awe.
“But a Dragonite?!” the Doctor cried, “Really! No way! With humans turning into Pokémon like these, I think I have a pretty good chance of turning out legendary!”
The Vulpix rolled her eyes.
Rory snorted. “Tell me about it!” he said to her, “What an ego!”
“Hey!” the Doctor protested, “I speak Pokémon, remember?!”
Rory and Amy shrugged at each-other.
“Well, why don’t you become a Pokémon now so things aren’t as confusing?” Amy asked, actually quite interested to see what he’d turn out as.
“Why not?” the Doctor asked with a grin, picking up the arch, “I bet I’ll be… A Palkia! Or a Dialga! Eh… no… Sort of bulky, huh? OOH! I know! I’ll be a Celebi! That makes sense, right? Time oriented Pokémon, loveable and awesome, and travel sized for our convenience?”
His companions just shrugged at him.
“Maybe,” said Rory.
“Makes sense, I guess,” Amy admitted.
The Doctor beamed. “I’m sure of it! I’m going to be a Celebi! These things are so easy to figure out! Predictable! Work perfectly every time using traits you already have so it can never deceive you…”
“I sure surprised him,” Rory pointed out, flicking his tail in annoyance.
“Foolproof!” the Doctor shouted, and slammed the Kecleon Arch onto his head.
A quick scream later, the Doctor was no longer a timelord and they had all been transported to a beach covered in bubble-blowing Krabbys.
Rory, mouth gaping open, and Amy, whose paws were clasped over her mouth, stared at the Doctor in utter shock, neither uttering a single word.
The Doctor twisted this way and that, trying to see himself, but couldn’t so he turned to the others. “So, go on! What am I? How do I look?!”
“Y-you’re…” Rory whispered, unable to do anything but stutter.
Amy, however, had finally gotten over her initial surprise, and was now rolling in the sand dying of laughter.
“What?!” the Doctor demanded, now a little bit more forcefully, “What am I Rory?!”
“AHAHAHAHAHAHAHA!” Amy laughed.
“Y-you…” Rory stammered, once again faltering.
“Tell me!” the Doctor begged him, wiggling with anticipation.
Rory burst into laughter too.
The Doctor continued to plead with them to explain what was going on, until Amy finally choked out, “S-see for yourself!” She indicated the nearby ocean, before falling over again, crying from laughing so hard.
The Doctor tried to stand up but couldn’t. Maybe it was an effect of the Kecleon Arch on timelords? He mentally shrugged it off and rolled to the ocean, which only made Rory and Amy laugh harder.
By now they were so loud that the Krabbys scuttled away and hid from the noise.
Finally, the Doctor rolled all the way to the ocean. He took a quick glance at his reflection…
And screamed louder than he’d ever screamed before.
He, the great and powerful Doctor of Gallifrey, the last timelord in existence, he who had defeated Daleks, Cybermen, Weeping Angels and everything else the universe threw his way had become…
A Magikarp.
He simply lay there, speechless, while his companions cracked up behind him.
The look on a Magikarp’s face when it is truly shocked is priceless, especially when the Magikarp is actually an especially proud timelord.
“The Kecleon Arch must be broken!” the Doctor cried.
“I- I don’t know Doctor!” Rory cried, “It’s- haha, very you! And you said it was foolproof!”
“I DON’T UNDERSTAND!” he roared, rocking over on his scaly side from the force of his shout. (Although it actually just sounded something like ‘karp, karp, magikarp…’)
“Well…” Amy said, finally gaining some composure over herself, (although she didn’t expect that to last long,) “You know what they say… You are what you eat!”
“What?” Rory and the Doctor chorused.
“Fish fingers and custard,” Amy explained.
There was a silence as they all considered this.
Finally, the Doctor spoke up. “Well, this will never do! How am I supposed to save the world like this?!”
“I don’t know…” Rory said doubtfully, flying over to him, “You must at least have some useful moves…”
“Yeah,” Amy agreed, “Show us! I can do this!”
She executed a perfect ‘ember’ move, the flames gorgeously licking the air.
The Doctor nodded in determination. “Well, I do know one move!”
The other two watched him in eager anticipation.
The Doctor rolled over the rest of the way into the ocean and began thrashing in the water about like he was having a seizure, sending a few stray droplets of water flying. “It’s called ‘splash’!”
Rory and Amy thought they’d never stop laughing again.

PokefanKala : Wow. Timelord = Majikarp ? Well this was funny , suspenceful and had a twist at the end . Good writng Loved it Buut I honestly thought a Mewtwo would suit the Doctor's Personality though  

Mr. Zed : Haha, thanks! It was just a joke, really. I really think the Doctor would be a good Celebi. Well... Then again, it was the 11th... But he's not useless really, more goofy. I guess he has being a Gyarados to look forward to?

Well I have watched Doctor Who a few times but my knowledge is minute compared to yours so you would probably make the better choice of Pokemon . And the first thought that popped up into my mind when he was reduced to A Majikarp was one of empathy . I put my self in his shoes ... or fins ... and then I thought ... wait ... I can beat up guys when I am a Garydos  So yeah . He does have that to look forward to  

Mr. Zed : Haha, I'm probably first on his hit list, just for that! XD