A/n: I couldn't find any Sixth Doctor crossovers with My Little Pony, so I am hoping this idea hasn't already been done. Thanks to Time Pony Victorious who beta-read this part! And these characters are not mine.
The Doctor moaned, lifting his head up from where he lay on the floor of the TARDIS. The last thing he remembered was a horrific jolt, and all his nerve endings feeling as though they were being shredded. Not unlike regeneration, really… wait. Had he regenerated?
"I don't feel any different," he murmured. "Hmm, I wonder…" He took stock of himself. "Same charismatic personality, commanding presence, strength of character and noble bearing… sea green hooves, limbs feeling a bit heavy but not worryingly so… sea green hooves!" The Doctor jumped up in alarm, landing awkwardly on hindquarters that were remarkably different from those he'd started out with. "Good heavens, I'm a horse!"
He slid forward on the floor, four legs splayed out, not prepared to test out these new limbs just yet. A glance behind him revealed a curly blond tail poking out of the striped trousers that had helped trip him up, trousers that were not designed for an equine body. He kicked them off pettishly.
"Time to take control of the situation, Doctor," he commanded himself, examining his new appendages with a critical eye. "It appears that I have taken on a horse-like form. Certainly I am now a quadruped, which is an entirely new experience for me. Well," he added with false brightness, "let's try standing up, shall we?"
He gathered his front legs underneath him and rose clumsily, standing on shaky limbs that rebelled against holding him upright. His first few stumbling steps got him over to the lever that opened the door of the TARDIS, and he was just congratulating himself on a job well done, when he realized he no longer had hands to grasp it.
"My kingdom for opposable thumbs!" he moaned, the irony of the original quote not lost on him. "I don't suppose you could help in any way," he huffed at the TARDIS. "Perhaps in the way of a big red button I could press!" He wrapped his front hooves around the lever, hoping the hind legs would stay planted on the ground while he made the attempt. He frowned at the faint sense of amusement lurking at the back of his mind-the TARDIS' reaction to his plight, but with one good heave (which again almost knocked him off his hooves) he got the door opened.
"Just don't lock me out when I return," he muttered to the ship, adjusted his coat as best he could, and trotted outside to find some answers.
The Doctor paused just in the doorway of a small shop, gazing about with a sense of wonder he hadn't felt in a long time as he watched the inhabitants of the town going about their daily lives. One unicorn ambled absently down the street, an open book floating in front of her as she read. The Doctor shook his head in amusement as three little ponies darted through town, doubtless up to some form of childish (foalish?) mischief…or running from the consequences of what they'd already done. A sky blue pony came up to him, carrying a basket of cupcakes in her teeth, which she set down in front of him.
"I've been trying out a brand new recipe. Would you like to try one?"
Tempting, but... "Thank you, no," he said. She answered his smile with one of her own and trotted over to the next pony she saw, who happily took her up on her offer.
The Doctor chuckled to himself. "A world of sentient ponies. Well, the universe is large enough to contain all kinds. I don't believe this the strangest thing I have seen, but it is certainly rare that I get the opportunity to go native to quite this degree." He reluctantly turned away from the activity of the street, calling out to the shop's owner in a louder tone, "Excuse me? Might I have some assistance, please? Just about every...pony I've come across has recommended I come to this establishment and ask for Rarity…well, with the exception of that rather exuberant pink pony who wanted to throw me a party."
(She'd enthused about his coat, too, as he recalled. Said it reminded her of balloons and confetti and just made her want to throw the biggest, bestest, most unintelligibly-worded party ever. Then thankfully she'd rushed off, leaving his eardrums ringing.)
The Doctor trotted through the door of the Carousel Boutique, peering at the contents of the shop. Thankfully there wasn't any need to open the door with his new, clumsy hooves. He'd had a hard enough time finding his way to the town, Ponyville, after he had left the TARDIS, tripping over his own four feet several times along the path. He had yet to acclimate to all the quirks of his new body and missed the strong, noble bearing of his usual Time Lord form. Still, of all transformations to be subjected to, this one wasn't all that bad. Quite a majestic form, really. He had to admit this new body of a young, powerful stallion suited him quite well, and on this beautiful day in picturesque Ponyville he couldn't help feeling in fine fettle...
"Be right with you, darling. Just give me a moment to finish up."
A white unicorn with purple mane stood with her back to him, her horn glowing with magic (not telekinesis, he reminded himself. The thoroughly unreasonable unicorn with whom he'd argued earlier had been fairly touchy on the subject) as a garment floated over to a dress mannequin. The Doctor snorted… maybe in this case it should be called a mann-equine?
"I'm afraid my business is rather urgent," he said, banishing the pun from his mind. He wondered why he'd been sent to what was obviously a dressmaker's shop. He'd assumed a library would be more along the lines of where he had to go to search out the information he needed. Then again, this could be the hub for local gossips, so maybe this shop was the place he could find information he couldn't learn in more conventional settings. "You see, I'm not quite myself and I was hoping…"
A shrill scream interrupted his request. The unicorn stared at him in horror, the garment she'd painstakingly been working on, lying crumpled on the ground. "Oh, how dreadful! Who could have done this to you?"
"Done to me? My dear young lady… er, filly, I assure you…" The Doctor stepped back, startled by her vehemence. True, he'd been changed into a pony, but from what he'd observed, ponies were the highest life form on this world. What problem could she possibly have with a magnificent specimen of horseflesh such as himself? He glanced down at himself, trying to determine what it was about his pony form that had caused her distress. Or…had her magic somehow revealed to her that he was not a true pony?
She studied him carefully, her horrified expression replaced with firm resolve. "No, no, I see why you've come. You were absolutely right to come to me. I promise, I will help you. Now just hold still. I can fix this. You poor darling!" Her horn began to glow, and a bright light enveloped the Doctor.
"What? Now just hold on a moment!" The Doctor squawked, clinging desperately to his multi-colored coat (and his dignity) in a bizarre tug-of-war as the unicorn's magic fought to strip the garment off his ponified person. Bolts of fabric floated above his head, waiting to wrap him in folds of soft, muted, tasteful color, while a tape measure snaked across his back a little too intimately for his liking. It was a battle of wills, and the Doctor was losing.
There were only two ways out of his current dilemma, sacrifice his coat to the determined unicorn, or run for the door. Using every ounce of his own resolve, he pushed back with his mind, sufficiently advanced mental ability warring against Rarity's magic. He gritted his teeth against unexpected pain as he concentrated, her magic unlike any telepathy he had ever faced before. Rarity faltered at his resistance, the bolts of cloth falling around him, no longer held up by the unicorn's power. The Doctor broke free and ran.
In his mad dash for the shop's exit, he took his turn too wide. Treacherous hooves slid out from under him. With a startled cry he skidded into one of Rarity's dress displays. He lay on the floor too dazed to move for a few precious moments, the dress form pinning him to the ground. Silky fabrics rained down over his body, the tangled garments further ensnaring him as he tried desperately to roll to his feet. Rarity moved to stand over him, and within minutes it was all over.
"We simply can't have you going around in this… this monstrous thing." Rarity cried triumphantly, her hooves firmly planted on her garish prize. "I cannot in good conscience allow you to be seen walking out my door in this nightmare of a coat!"