The Darkness works in many ways, shapes and forms. Not only does it use set-piece armies that sweep over entire lands, destroying all opposition along the way, but it also uses subversion, coercion and other... shall we say, pursuasive tactics, to fight its battles. One of these 'tactics' are named simply, the Shadowrunners.
The Shadowrunners are a group of mysterious, dark beings, no one knows their race but many presume a type of elf, that are more or less a group of highly trained, highly dangerous assassins that kill for the highest bidder. It is not known why or when the Shadowrunners joined the Darkness, but it is known when they entered the playing field. They entered by 'silencing' a number of royal family members in a kingdom to the east of the Darklands.
Needless to say, the assassinations were meer milk runs to what the Shadowrunners were used to. In one climactic battle during a war between two of the major human kingdoms, the Shadowrunners appeared suddenly during the battle and began decimating the command structure of the Mandalains. Their king was first, the Shadowrunner's leader, only known as the Shadow, appeared beside the king and his horse and began to relay infomation to the king, laxing him into a false sense of security. When Shadow had the king right where he, or she, wanted him, he struck by piercing the king's heart with his/her Shadowblade, which was infused, by use of dark magic, with certain posions and spells that worked its way into the victim's bodily systems, killing them slowly or quickly per the user's preference. Ever since, the Shadowrunners have been enemies of the state or a glimmer of hope for a nation bewrought with war that begins to crumble.
But it is known which side they support now. And no one knows why. But some know this: They are on the move once again. And no one knows to where.