Dungeons & Dragons: Dungeon Module S2 "White Plume Mountain"
Steve: You float out into a cavern and the path ends in a boiling chamber of steam and mud. It seems as if the only way is to cross and to do that you have to climb over some dangling tables on chains. Beneath you is a lake of boiling mud, so if you fall you're going to die. Geysers of mud erupt and splash on the tables hanging from chains.
Zack: Who designed this place? Whatever. Buddy Jones rolls in fog mode.
Steve: It doesn't say anything about gaseous form in the book.
Zack: Mess with the gas form, get the vapors.
Steve: You drift across the boiling lake effortlessly.
Zack: I fog-strut around contemptuously when I get near the other side.
Steve: The boiling mud like looks pretty ticked. Your gas form wears off when you get to the other side.