Amulet of Life Warding (5e Equipment)
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Wondrous item, very rare (requires attunement)
This amulet has the power to preserve and protect your life force. While you wear it, you have immunity to necrotic damage.
Additionally, if you drop to 0 hit points while you are wearing the amulet and don't die outright, you regain 100 hit points. Once you have used this power of the amulet, you can't use it again for 7 days.