The Nanoplague

Plague / Epidemic

The Nanoplague lasted only 5 years, but it radically re-shaped the face of the planet. Over half of the general population was wiped out during this time, with almost all being affected on some level by small mutations. A percentage were horribly transformed into terrible monstrosities, roaming the planet later as Variants.   Thankfully, the Nanoplague was engineered to burn itself out quickly by it's creator, the sentient AI Taurus. Once the plague affected a creature, it wrote markers into the DNA of the creature that prevented further changes.