pl. n. rust monsters
n., in Dungeons & Dragons, a usu. non-lethal monster resembling a bumpy crustacean with a propeller on its tail; the creature turns valuable metal objects to rust by touch, and then consumes the rust; c. early 1970s.
Addendum: Designed by Gary Gygax before the first edition of D&D was published; apparently based on a bizarre plastic figure he found in a toy set marked “dinosaurs.” The monster was meant to be more of an annoyance than a threat, presenting a danger to the party’s hard-won loot.