Ulthar's Portable Phylactery

When a creature within 30 feet of you is reduced to 0 hit points, you can use your reaction to capture its soul in a sealable container you possess, The container becomes a temporary phylactery, trapping the creature's soul and preventing its death. 

Suspended Death: While the soul is contained within the phylactery, the creature's body remains in a state of suspended animation, appearing dead but not decaying. The creature is considered stable and does not make death saving throws, but it cannot be revived, healed, or affected by any spell or ability that targets the living or dead.

Soul Release: At any point during the spell's duration, you can use an action to release the soul back into its body, regardless of its distance from the phylactery, as long as it is on the same plane of existence. The creature returns to life with hit points equal to half of its maximum hit points.

If the phylactery is destroyed or the spell's duration expires, the soul immediately returns to its body if it is still intact and within 300 feet. If the body is destroyed or beyond this range, the soul is lost, and the creature is considered permanently dead, only retrievable through the most powerful magic, such as a wish spell.