Chaos phage

Chaos Phage is a magical disease most commonly inflicted by Blue Slaad, a race of creatures originating from the Chaos Plane. The disease was slow acting but incredibly fatal, and usually killed its host within days, causing them to rapidly wither away.

People killed by the disease would be reborn as Red Slaad. Spellcasters capable of casting spells 3rd level or higher would instead be reborn as a Green Slaad.

The disease can only be cured by magical means, and the transformation can only be undone by a 'Wish' spell.