Well, I'm here for the same reason I'm on Fanfiction.net: to get rid of all the ideas that stop me from working and hopefully entertain you all in the process.
Dark Saber is the former guardian of the Princesses, exiled after the Nightmare Moon incident. He now lives as Winter Shield in Ponyville. How will he affect the MLP universe? Who knows? I sure don't. Let's just read and find out...