Those who were struck a non-lethal blow by the sword had a chance of being inflicted with wererat lycanthropy. In addition, the wielder could summon and control a horde of rats, or a small number of giant rats.
The first noted appearance of Calathangas in Faerûn was in the hands of the Battledalesman warrior Rathinor in the late 13th century DR. In the years when the Dalelands were hit with a devastating plague, Rathinor fell in combat while driving off a band of thieves. It disappeared for about 15 years, before a peasant sold it to a ruthless soldier named Xerastos, for the price of six sheep. Xerastos' renown as a combatant grew quickly, due in no small part to his prowess with the cursed blade. A decade later, Calathangas exchanged hands again as Xerastos was killed by a paladin who sought to destroy the then-infamous blade. Unfortunately, the paladin fell ill before completing his quest and the sword had not been encountered since.