Blood Mark

Used as a form of currency between undead lords and the humanoids of their lands, this coin resembles a gold ring with a single hole in the center. It holds 1 charge, visible as a red glow in the center of the coin. While holding the coin, you can use an action to expend 1 charge and regain 1d3 hit points. At the same time, the humanoid who pledged their blood to the coin takes necrotic damage and reduces their hit point maximum by an equal amount. This reduction lasts until the creature finishes a long rest. It dies if this reduces its hit point maximum to 0. You can expend the charges in up to 5 blood marks as part of the same action. To replenish an expended charge in a blood mark, a humanoid must pledge a pint of their blood in a 10-minute ritual that involves letting a drop of their blood fall through the center of the coin. The drop disappears in the process and the center fills with a red glow. There is no limit to how much blood a humanoid may pledge, but each coin can hold only 1 charge. To pledge more, the humanoid must perform the ritual on another blood mark. Any person foolish enough to pledge more than a single blood coin might find the coins all redeemed at once, since such redemptions often happen at great blood feasts held by vampires and other undead.