Amulet of the Lifeblood

This amulet has the power to preserve and protect your life force. While you wear it, you have immunity to necrotic damage.

Your hit point maximum increases by an amount equal to twice your level when you gain this feat. Whenever you gain a level thereafter, your hit point maximum increases by an additional 2 hit points

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.