Source: Lost Laboratory of Kwalish

Weapon (any sword), rare (requires attunement)

Choose a magical bonus of +1 to +3. This sword gains that bonus to its attack and damage rolls. For each point of bonus you choose for the sword, you take a corresponding penalty (−1 to −3) to your death saving throws. You can change this magical bonus each day at dawn.

Curse. This weapon is cursed, and becoming attuned to it extends the curse to you. Until the curse is broken with a Remove Curse spell or similar magic, you are unwilling to part with the weapon.