The Doctor shouldered his way into the Tardis as an energy bolt whizzed past his head, impacting with sparks on the center console. "Not a very friendly greeting!" he yelled out to the alien creature that continued to take shots even as the door was closed. The Tardis sprang to life on its own, seemingly unhappy about being shot at. A distinctive noise was heard as the blue police box pulsed, fading from sight.
The Doctor rushed to the center console flipping a switch and rotating a dial.
"And what do you think you're doing?" he queried towards the machine. To this the switch he had moved flipped back with a slam and the dial spun wildly. The Tardis became unsteady and the Doctor was pulled against the wall, like a spinning gravity ride.
He attempted to use his sonic screwdriver, its whir barely distinguishable through all the noise. The Tardis leveled out and his feet slid back to the floor. It was then that he felt a familiar sensation as the Tardis forced a strange transforming energy into him. "Why Equestria? I'm in the middle of saving a solar system here... I don't need a vacation!" The Tardis shook violently, tunneling its way through to another universe and dimension. Equestria was a hard place to get to, apparently.
The Doctor folded over in moderate pain as he shifted. His form slowly changed into that of an earth pony with a chestnut brown mane and a light brown coat. As the transformation completed itself, he shook his head to forget the pain he had just felt. Apparently he had arrived, as the Tardis had ceased its motions. This pony transformation was only a temporary thing; it would last until the Tardis decided to change him back.
"Hooves...” He lifted his forelegs, “check, mane?” He looked to a semi reflective piece of metal. “Still not ginger, Oh well. Teeth. What about teeth?" He smiled to his reflection.
“Everything seems to be in order. Wait, clothing? Different story..."
He trailed off , looking upon his ruined clothing with a frown and shaking off his ill-fitting slacks. They weren't damaged as badly as the shirt, though. He put a hoof into a tear hole and finished the job, letting it fall to the floor. Luckily his suit had fallen off earlier and was not ruined. He left the bowtie for good measure, giving it a quick straightening. "Bowties are cool after all, even on a pony," he spoke to himself.
"Cutie mark? He finished his checklist and stared back at his flank, a sand filled hourglass upon it. "Still got it after all this time away."
The Doctor reminisced about his first time accidentally finding this world. The transformation process had been very startling his first time, but stranger things had happened before. Every visit after throughout the years was a little easier to cope with. Every time her regenerated, the Time Lord way of cheating death, his pony form would change as well.
The Doctor opened the door to the Tardis, peering out he saw he was in the bowels of some cave system. His hooves clacked against the ground sending echoes throughout the dank and stuffy cave. The Doctor, adventurous as always, headed off into the dark to find what new adventures awaited him.
The tunnel eventually led to a large stone cavern. The cavern was dimly lit with torches along the wall, and as the Doctor advanced a gruff voice spoke out.
"Who would dare disturb Lord Discord?" A large bipedal dog with short legs and long muscled arms approached him.
"Ooh! And what might you be?" The Doctor queried. "I never have seen a creature quite like you."
"Allow them forward!" a voice called out in the dark.
The Doctor moved through the dim haze peering at a shadowed figure on a twisted throne. A few torches flickered into existence as the Doctor approached. The figure on the throne was a mixture of animals: he had the foot of a dragon and the other was of a goat, one clawed hand of a bird of prey and the other of a lion, his yellowed eyes with red irises peered at the Doctor.
"A chimera!" The Doctor exclaimed almost happily. "I haven't seen one of your kind in quite a while, let alone a draconequus."
Discord's attention was awoken entirely at the Doctor's last word. "Who are you to know the name of my kind?"
"I'm The Doctor."
"Doctor Who?!" the Chimera responded sounding annoyed.
"Exactly! Doctor Whooves!" The Doctor joked, making a play on his name, chuckling to himself.
"And who is it you think you are that you do not bow to His Royal Highness, King Discord?" the Dog rebuked.
"I've never been much for bowing," The Doctor replied.
"Tell me Doctor, you are not from here. Am I correct?"
"Neither are you, from what I heard your kind was extinct."
"This world was... inviting. I have power here, unchecked, unfettered. I have more power here than anywhere else in the universe, enough for me to live for an eternity. And a world such as this needs balance, all this harmony needs a little chaos and destruction."
"I am sorry, but I have already helped save this land once. I cannot let it fall into the hands of a power hungry tyrant."
"And you think you can stop me?" replied Discord. "Kill him," Discord dismissively spoke to the dog.
The Doctor backed up while pulling out his sonic screwdriver from under his bowtie strap, holding it in his mouth. He activated it, the frequency reverberating through the room. The dog ceased its advance, covering its ears and pitifully whining at the sound.
The ceiling shook, and rock began to fall. The Doctor turned, galloping back to the tunnel to avoid being crushed. Just as he entered a tremendous rockslide tumbled over the entrance.
"I'm so old now. I used to have so much mercy." The Doctor sighed, tucking the sonic screwdriver back in his bowtie strap. It wasn't every day you were forced to finish the extinction of a race. He had hoped that this one could be saved, but Discord, as he had named himself, was just like all the others of his kind, tyrannical and now dead.
The Doctor slipped his way back into the Tardis. "Come now, I'm finished here." He snapped to the living machine. It whirred to life and the Tardis vanished from view. The Doctor knew there must be something more to be done in Equestria, something important otherwise the Tardis would never have forced him to come.