Lighning guards are special boss mobs located in the area outside your city. They are pretty much impossible to defeat even with very high level heros without the use of an item called "lightning card". These cards can be purchased from the mall for 35 points and turn the god-like lightning guards into "weakened lightning guards", oponants easily defeated by even a low level solo hero. Once defeated lightning guards drop a random purple item, the level of which is determined by your progression age (level 60 gear at empire age). Once the 5 lighting guards are defeated, no more will ever spawn so resist the urge to kill them before empire age.