Have you ever stopped to gaze up at the sky, enjoying the sheer beauty of it all? When you are watching the slow movement of the clouds, and soaking in the warmth of the sun, ever notice something shimmering slightly in the corner of your eye? You may try your best to discover what that shimmer might be, or to catch another glimpse, but it would be futile. The moment you turn your head to focus, it zips off in another direction, never to be seen again.
Someponies may say that it was a trick of the light, or perhaps dust in your eye. While others would direct you to a doctor to get your vision checked out. Both would be wrong.
For there is a story to go with this strange phenomenon, and it is quite the tale indeed. For that is no mere illusion born from Celestia's sun, or a stray piece of dust. It is actually a pony, and his name is Sky Shimmer.