[Variant] Helm of the Undying (Patreon)

(Wondrous Item), uncommon (requires attunement by a Creature of Evil Alignment)

This old iron helmet is covered in scratches and mosses from past battles. It’s enchanted by old evil magic that can make you very hard to kill. When you attune to this magic helmet, you gain advantage on death saving throws.

In addition, once a day, as a reaction to succeeding in the third death save, you can immediately expend any number of hit dice.