Plague Slinger is a medium armor set. When you take damage, you summon a Skeever corpse which will launch a poison ball that deals 5160 Poison Damage every 1.5 seconds at the nearest enemy for 6 seconds. This effect can occur once every 15 seconds.
The Plague Slinger set is part of the Dragon Bones DLC. It drops in Scalecaller Peak in Stormhaven. Each set item is bound on pickup. You can acquire medium armor, weapons and jewelry of this set in the Scalecaller motif style.