There is a quest in Stormhold that gives a weapon that procs. Still got to get the drop to start it though, so haven't seen that weapon myself.
The quest starts from a random, rare drop in StormHold. Rarely, a mob (cavaliers and crusaders confirmed) will drop the Sword of Thunder. Examine it and you get the quest Berik's Revenge.
Kill 100 skeletons, any type seems to work.
Examine the sword again and you will be prompted to kill three named mobs.
Kill Blacksmith Brigg. He is on the top level. Defiled locksmith is his placeholder.
Kill Battlepriest Alexandria. South at atrium. Right at the water. First door on right. Defiled Torrent is the placeholder.
Kill Defiled Lord Byron.
Courtesy of Tentonhammer guild for guide to this quest, but I`ve never seen the weapon myself