Not your typical Doctor Whooves fanfic. A series of events cause the TARDIS to blast into a dimension populated by (you guessed it) ponies and (of course) crashes. While waiting for the TARDIS to repair itself The Doctor runs across a certain brown stallion, whom he will discover is a reflection of himself in more ways than one.
But even after The Doctor was gone his mere presence created a ripple that would awaken an ancient being. Continued in the sequel http://www.fimfiction.net/story/15733/Doctor-Whooves-and-the-Sea-of-Dreams