Light and Shadow is a fanfiction written by Comet Chaser, an up and coming author with few known works.
Light and Shadow is a story about the OC character Shadow Chaser and his adventures through Equestria at large. The story also has heavy involvement of some of the less expounded upon characters in the actual television series such as Princess Luna and Vinyl Scratch. One of the largest points to note for this story is the fact that the author makes a very heavy effort to make sure the story fits into the canon, particularly the point between seasons 3 and 4. This story also updates weekly under normal basis, but is currently on hiatus.
There are actually two versions of Light and Shadow, the original done only by Comet Chaser on ponyfictionarchive
And also the "improved" version which is edited by SkullTX avaliable on fimfiction