Death and Decay is a signature spell of both the Death Knights of Warcraft II and the Liches of Warcraft III. It is a necromancy spell.Template:Cite It appeared to be some kind of spell that saturated the air with acidic chemicals that ate through armor, stone and flesh. Teron Gorefiend - while he has possession of your body in Shadowmoon Valley - can cast this spell against his jailer Karsius the Ancient Watcher, and some mobs in Scourge-controlled areas such as Razorfen Downs utilize this spell.
Background
Death and Decay in action.
Teron Gorefiend using Death and Decay on his Jailer.
The aphotic, swirling clouds conjured by the Death Knights can cause anything within their path to rot and decompose. The vapor created by Decay can consume anything - flesh, bone, wood or even the strongest metal. Heavily laden with base substances, these clouds descend and quickly diffuse, leaving only suffering in their wake.Template:Cite
The swirling negative energies known as the Death And Decay spell are favored by the liches for their power to decompose, rot and destroy everything within them. Not even the strongest warriors or the most durable structures can stand the full effects of Death And Decay.Template:Cite
Negative energy infuses the area in visible puffs. Living creatures age rapidly, as skin sags and flesh sloughs off bones. Structures wither and collapse, suffering the effects of decades within a few seconds. All living creatures and non-natural structures in the area take damage from the negative energy. Since undead are powered by negative energy, this spell cures them a like amount of damage.Template:Cite
In World of Warcraft
In-game, the spell is used by the mobs:
- Death's Head Cultists, quilboar casters outside the Razorfen Downs
- Sunseeker Gene-Splicers in the Botanica, Tempest Keep
- Rage Winterchill, a lich boss in Battle for Mount Hyjal
Wrath of the Lich King 
- Main article: Death and Decay (death knight)
Death and Decay is going to be a spell for the new Hero Class, the death knight. It will cause AoE damage and have an additional chance to fear targets within the area of effect. It also serves to gain threat on multiple mobs too.[1]