Dark Sun: The Scorched World of Athas
The abyssal plague is a disease that has periodically appeared on Athas, although very few facts are known about it. Those infected by this disease slowly develop oozing sores, blisters, and growths that appear to be made of dark red crystal with silver veins and gold flecks. The crystal can be in either liquid or solid form.
Initially the infected have increased prowess in physical combat but their overall health suffers. As the disease progresses and the crystal spread to more of their body, their health fades further even as their body hardens against physical damage. This continues until the crystals cover their entire body and they are consumed.
Outbreaks of the Abyssal plague, though rare, have had devastating consequences. Entire villages have been put to the torch to prevent its spread. Each outbreak of the abyssal plague is marked by the appearance of a strange dark red crystalline growth on the victims, in either solid or liquid form. The crystals appear to be laced with silver and flecked with gold. Infected creatures gain both unnatural strength and a desire to destroy all living creatures.
The Abyssal plague is highly contagious. Even if only one creature catches it from a plague demon, the plague can infect those who travel with the afflicted companion, eventually spreading the disease throughout the world.
Those who have survived the plague have said they experienced a vision of an enormously powerful entity trapped in a void of darkness and desolation. While the plague grew stronger, the victims heard the whisper of this entity and became filled with a desire to destroy every living creature.
The phrases invoked by those infected come from a foul, ancient language. No direct translations can be made of the more complicated phrases, but the simpler phrases speak of a world of complete darkness, devoid of life, and an insatiable hunger for destruction that has existed since the beginning of creation.