I just killed a thrall (regular thrall, not cursed) & he exploded into a ball of lightning that took out half the health of an adjacent thrall. If was like the firefly perk but with lightening instead of fire Edit: After paying a lot more attention I've found 2 guaranteed hidden perks on thunderlord. Outlaw & firefly! Precision kills speed up reload & from my guess, there's about a 20% for targets to explode with lightning! I was never crazy about this gun, but now I can't help not be! It's the machine gun version of Fatebringer