Not really fan-art, because most of this is a screen capture of the My Little Pony episode "Winter Wrap Up" during the Winter Wrap Up song.

The pony in the center is a generic space-filler pony, one of many that Lauren Faust's team created for the Friendship Is Magic series.  However, he bears a striking resemblance to David Tennant, who played the Tenth Doctor in Doctor Who, and his cutie mark is (randomly, we're told) an hourglass.

I couldn't help but photoshop a tardis into the scene.