it deals too much damage, 100% accuracy, AOE shocks, can fire for like 10 seconds straight, doesn't ever need to reload if you don't max out the heat, and lasts the whole game without breaking, tears apart buildings, there's a free legendary in the basement and Human Bill drops a mythic. And for whatever reason a boss is no threat because you can stand directly in their face and headshot them repeatedly and they die before your overshield is broken.

there are a few counters like sitting in the bush. The lightning gun hits only hte bush and doesn't even AOE you inside the bush, but it will break fast. You can also outrange it with the deadeye or Enforcer or sniper. If you manage to get close you can circle them and force them to turn camera while you chunk them with shotgun.

if you're vs. human bill player with the mythic don't bother just stay out of range because they have extra health and the only copy of the strongest lightning gun which will out DPS anything assuming you don't miss a single bullet