Steam vortexes leave behind a trail of non-poisonous, temporary clouds behind them as they move. When they are killed, they burst into a large cloud centered on the spot where they died.

Fog horn, a magical tool that when played surrounds the user with clouds and possibly fog clouds (the monster). It would be best if some type of non-poison-gas cloud were implemented first; it is probably a bad idea to actually change the terrain around the user into cloud.

Assuming the game supports creating temporary regions of non-poisonous gas clouds: New “smoke bomb” potion. It makes you choke/vomit when quaffed. Intended to be thrown; where it shatters, most of the surrounding terrain will be transformed into cloud.

Vanilla has since added non-poisonous gas clouds (for things such as mist from zapping fire over water), and this effect could work just as well by breaking a smoky potion, instead of adding a new object.