Maca-Tlam's Fang

This large tooth is seven inches long, one inch wide at the center of its base, and is gently back-curved, with razor-sharp serrations on both front and back edges. The creature it belonged to was obviously a massive reptilian predator of some sort. Close examination of it with magic reveals that it lacks any obvious imperfection or growth lines, and while it does not seem to be magical it exudes a faint aura of despair and rage, to those with a sufficiently honed empathic sense.
The fang was given to a party of adventurers by a spirit within an ashen dream-world; they were told to drive it into an idol of Tar-Vash they had looted previously from a band of Ripfang warriors, and that doing so in the right circumstances would deal a blow to the Ripfang's lightning god.