Call of the Dark is a 13th level cleric Encounter power that was introduced in Heroes of Shadow.
Call of the Dark
Cleric Attack 13
As your allies close in, a black cloud surrounds your enemy to signify its inescapable doom.
Close burst 3
Target: One enemy in the burst
Effect: The target grants combat advantage until the end of your next turn. In addition, the next attack made against the target before the end of your next turn deals 3d8 extra damage on a hit or a miss, even if the attack normally deals no damage on a miss. This extra damage cannot benefit from bonuses to damage rolls.