Hellfire Blast

Whenever you use your eldritch blast ability, you can change your eldritch blast into a hellfire blast. A hellfire blast deals your normal eldritch blast damage plus an extra 2d6 points of damage per class level. If your blast hits multiple targets (for example, the eldritch chain or eldritch cone blast shape invocations), each target takes the extra damage. This damage is not fire damage. Hellfire burns hotter than any normal fire.

Each time you use this ability, you take 1 point of Constitution damage. Because the diabolical forces behind the power of hellfire demand part of your essence in exchange for this granted power, if you do not have a Constitution score or are somehow immune to Constitution damage, you cannot use this ability.