Source: Bigby Presents - Glory of the Giants

Wondrous Item, Very Rare (Requires Attunement)

A black opal pendant hangs at the base of this pearlescent chain. The sacred rune is inscribed on the back of the pendant.

While wearing this item, you have resistance to necrotic damage. Additionally, you can cast the Spare the Dying cantrip using either an action or a bonus action.

Invoking the Rune. When a creature you can see within 60 feet of you is reduced to 0 hit points as a result of taking damage, you can use your reaction to invoke the item’s rune, causing the pendant to flash with pale light. The creature then instead drops to 1 hit point.

Once the rune has been invoked, it can’t be invoked again until the next dawn.