The curse that was around Sevenarches that supposedly stopped affecting the surrounding area after The Missing Moment happened. This is the curse that effects only elves.
The shadewither key had this curse attached to it.
When elves contract the curse they first begin to cough, then they fall unconscious. Over several days they then slowly blacken and start to shrivel up like rotting fruit until they die. A corpse made this way becomes dry and charcoal-like, collapsing at the slightest touch.