Widowmaker is a medium armor set. When your alchemical poison fires, you drop a poisonous spore in front of you that bursts after 1 second, dealing 7740 Poison Damage to all enemies within 5 meters.
The Widowmaker set is part of the Shadows of the Hist DLC. It drops in Cradle of Shadows in Shadowfen. Each set item is bound on pickup. You can acquire medium armor, weapons and jewelry of this set in the Silken Ring motif style.