The volcano-world's founding catastrophe: Scolopendra's nine-tiered poison cloud that killed or transformed its people.
The cataclysm is the founding catastrophe of the Over City's children's-story backdrop, retold to Carl by Tsarina Signet. Scolopendra — the monster at the bottom of the volcano — unleashed a poison cloud that was a 'Nine Tier attack,' striking in nine different ways at once: the lucky simply died, while the rest were transformed in myriad ways. It devastated ninety percent of the volcano-world.
Among its victims, Grimaldi became the vine whose spores now control and regrow the transformed circus creatures; Signet alone of the troupe passed through the cloud unaltered. The event explains the monsters roaming the Over City Ruins and the villagers descended from survivors.
The floor's origin catastrophe, the source of its monsters and its central quest.