
(Wondrous Item), artifact (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 grant you true immortality, in exchange for your mortal body. When you attune to this magic helmet, your body withers to the bones. Then from the helmet, a new body is formed. You keep all abilities you had in the previous body, but now you are undead in addition to your other race, and you can’t remove the helmet as it became a part of you.
Having 0 hit points doesn’t knock you unconscious. You still must make death-saving throws and suffer the normal effects of taking damage while at 0 hit points. Once a day, as a reaction to succeeding in a death save, you can expend any number of hit dice. If you do, for 1 minute, you gain resistance to all damage except psychic and cold damage, and your weapon attacks score a critical hit on a roll of 18–20.
If you would die, instead, your body disintegrates along with the helmet. In the next dusk, 5 feet from your original bones, a new helmet is formed, and you return to life with a new body and one level of exhaustion.
You cannot return to life if your original bones are destroyed, kept underwater, or your immortality is removed by a wish spell.