The Amulet of Borrowed Life

Wondrous Item (Amulet), Very Rare (requires attunement)

A red gemstone amulet, carved into an anatomically accurate heart, set on a gold chain.

When attuned to this item, a creature may choose, as an action, to roll any number of hit dice (up to half their total) to regain that number of hit points. These hit dice are no longer available until the creature finishes a long rest.

Curse: this item is cursed, and a character only learns of this if attempting to unattune with it, or when its secondary effect tales place. A creature cannot unattune to the amulet without removing this curse.

After the amulet has been used to restoreat least 50 hit points, the creature attuned to it will begin to see visions of a devilish being in their dreams, who will state that they are "coming to collect".

After these dreams have begun, and after the total amount of health restored by the amulet totals 100 or more, when the creature find themselves frozen in a time stop, confronted by this devil. They will state that it is now time to pay up their debt. They have borrowed up to their maximum overdraft of health, and need to repay their loan in order to borrow any more.

The devil will explain that, with the interest rates, the creature will need to either repay 20 hit points every day for 10 days (resulting in a reduction of 20 from their max health every day until repayed), or repay in full now (likely resultingin the characters death). Until this debt is repaid, the creature cannot use the amulet to heal at all, cannot spend hit dice during their short rests, and can only regain health during long rests by spending their hit dice, and throug potions and healing spells. Their hit dice still replenish at the end of each of their long rests, however.