Erinyes

If the monster dies outside the Nine Hells, its body disappears in sulfurous smoke, and it gains a new body instantly, reviving with all its Hit Points somewhere in the Nine Hells.

The monster has Advantage on saving throws against spells and other magical effects.

The monster has a magic rope. While bearing it, the monster can use the Entangling Rope action. The rope has AC 20, HP 90, and Immunity to Poison and Psychic damage. The rope turns to dust if reduced to 0 Hit Points, if it is 5+ feet away from the monster for 1 hour or more, or if the monster dies. If the rope is damaged or destroyed, the monster can fully restore it when finishing a Short or Long Rest.

The monster makes three Withering Sword attacks and can use Entangling Rope.

Trigger: The monster is. Response: The monster adds to its AC against that attack, possibly causing it to miss.

Melee Attack: +8 to hit. reach 5 ft. Hit: 2d8 + 4 slashing plus 2d10 necrotic damage.

Strength Save: DC 16. target: creature. Failure: 4d6 force damage.