Demons are creatures from Hell, usually sent here to reap destruction and slay the enemies of their evil masters, while at the same time collecting new souls for their home world. Demons take many shapes and sizes, often taking the form of the worst nightmare of their current enemy.
Burning Legion: the Lord of Hell works in mysterious ways, that much is certain. In the quest for mortal souls, he sometimes prefers subtle and devious plots that might take centuries to unfold. At other times, however, when an opportunity presents itself, he will not hesitate to unleash the horrible forces of Hell--to burn and kill, to desecrate and destroy everything in their path. If four or more players on a team are demons and/or heretics, they will be considered a Burning Legion, and will receive extra bonuses (see the help files of the different classes as to the nature of these bonuses).
Fireshield (Burning Legion only)
This ability granted by the Lord of Hell is probably what the Burning Legion is named for. It works much like the spell of the same name (see "help spell fireshield"), but can only be used once per minute. (Demons who already have this ability will not be granted this bonus, nor do they need it.)