Hellfire

Hellfire is an PBAoE spell during which pulses of fire radiate out each second from the caster, causing damage to enemies within range and the caster himself. This spell is a channeling spell, so interruptions can shorten the duration and thus the damage output.

Utility
Hellfire is an optional finishing move for Affliction Warlocks when Drain Tanking. However, it should only be used against green-level creatures unless there is a healer around, for it will usually damage the caster more than the mobs are.

Warlocks are unable to resist the damage that Hellfire does to themselves unless they use the Sacrifice ability of the Voidwalker, then the shield will take the damage until the shield fails or the effect is interrupted by moving.

If the warlock dies from this spell's effect, they take no durability damage. This allows the Warlock to save some repair costs when faced with certain doom. In such a scenario, a Warlock will typically use life tap to get low on health fast, then use Hellfire. This is commonly referred to as "Ghost Walking" and is a common way to get into Scholomance without possessing the Skeleton key.