This old wizard really ruined Saventh-Yhi. The seeded the city with spores that made everyone insane with paranoia. He also built a series of vaults around the city because the end of the world was coming and the people needed a place to stay. However he heavily laced these with his spores.
Eventually he succumed to the spores himself. The PC’s learned all of this from his journal they found in his lab in the first vault.