Petrifying Cloud

Petrifying Cloud is a monster-only spell which emits a stream of clouds of calcifying dust, dealing minor damage on impact. Anything that ends its turn inside a cloud has a chance to start petrifying. The higher your XL (HD for monsters), the less likely for the petrification attempt is to be successful.

For players, those who are a Gargoyle, in certain forms (Statue Form, Shadow Form, Storm Form, Wisp Form), or under Zin's Vitalisation are immune to petrification, while Qazlal makes you immune to all clouds. You'll still take impact damage, though. For monsters, gargoyles, statues, insubstantial monsters, earth elementals, and catoblepae themselves are similarly immune.