The stand-alone expansion, named Might & Magic Heroes VI: Shades of Darkness, was released on May 13, 2013. Unlike the original game and its DLC, Shades of Darkness was developed by Virtuos. Its main protagonist is the Dark Elf Raelag, who first appeared in Heroes of Might and Magic V, and features the return of the Dungeon faction, led by the Dark Elves. New additional content is also available, such as about 20 new neutral creatures, 10 new buildings and three new artifact sets. There are also expected to be notable changes to the multiplayer wing, especially the way players connect to the Conflux and a redesigned Legacy weapons system.
Source: Wikipedia, "Might & Magic Heroes VI", available under the CC-BY-SA License.