hehe..
so, at the end of the quest when you're fighting the boss in the dark, the special version of the quest that we're going to get for our swords will have 3 Knights during the boss fight. Each Knight represents a different element and will have shields corresponding to said element. The goal of the quest is to kill our respective elemental Knight within 30 seconds of killing the boss ( I think we need to kill the Knights first, then the boss ) .. so essentially during the entire boss fight we'll need to go without killing our knights until the boss has low enough health. The quest becomes harder the more people you have doing the different elements because it means more knights will be up the entire time.
Basically since you and I have void/arc, we can kill the solar one (unless our 3rd teammate has a solar sword) and leave the other 2 up until the end.