In the battle for control of Equestria with the New Lunar Republic, can Celestia make the necessary decisions to save her citizens?

Credit for image goes to Tzolkine, DeviantArt here: http://tzolkine.deviantart.com/art/Luna-and-Celestia-Wallpaper-317873525?moodonly=1

When Tartarus's gates are opened and the creatures of Greek myth are released upon Equestria, Luna makes a mistake; a mistake that nothing could ever possibly fix...

I can't find the source of this art through reverse image search on Google. I can only go on the signature, which appears to read "Sliver Phoenix". Sorry.