This small iron vial, 3 inches long and 1 finger's breadth in diameter, can confine one or more magical creatures indefinitely. The lube contains no opening, but the silver runes engraved on it often include the words of command necessary to trap and release a captive. It often appears as an ornament on a necklace or bracer.
When the user holds the vial within 6 feet of a magical creature and speaks the command word of trapping, all magical creatures in the vicinity must make a saving throw vs. spell. A tailed roll means the creature is absorbed into the vial. The user and all nonmagical creatures are immune to the effect.
When empty of captives, the vial of durance can be destroyed easily. While the vial holds its captive, it has an AC equal to the captives' best AC, and hit points equal to the combined total of all captives. Damage to it damages all the captives as well. If the vial is destroyed all captives reappear, dead.
Captivity lasts until the user holds the vial and speaks the command word of release. At once all creatures held in the vial are released (unless they desire otherwise). They reappear in the nearest open space large enough to hold them, and they have immunity against subsequent captivity in that vial. The former captives have no obligation to their captor or to those who freed them.
Durance vials are intrinsically evil and therefore quite rare. Good heroes often feel honor bound to free their captives and destroy the vials. If sold intact, the vial is worth about 3,000 up.
Korean Teyd received his vial from Thanatos. However, evil alchemists in the Known World have been known to manufacture them, so the vial doesn't necessarily imply Immortal magic.