Source: Tal'Dorei Campaign Setting Reborn

Wondrous item, very rare

This black crystal pendant is a magical gateway to a small pocket dimension. You can use the pendant as an improvised weapon to make a melee or ranged weapon attack against a Large or smaller creature. On a hit, the target must succeed on a DC 10 Wisdom saving throw or be trapped within the crystal. A creature that wants to be trapped can intentionally fail this saving throw.

Only one creature at a time can be held in a raven’s slumber . That creature is aware of the passage of time and can see the world outside of this talisman as if through a window. You can release a held creature to an unoccupied space within 5 feet of you as a bonus action.

If a companion creature granted to you by a class feature, or a beast that you’ve tamed as a companion, is reduced to 0 hit points while within 100 feet of you, it is immediately drawn into the pendant and stabilized. If the pendant already holds a creature, this effect fails.