Enervating Crystal Sword (Patreon)

Weapon (any sword), rare (requires attunement)

The blade of this sword is made of a sickly green crystal. It pulses with an unsettling light while held, which sheds bright light in a 10-foot radius and dim light for an additional 10 feet. You gain a +1 bonus to attack and damage rolls made with this magic weapon.

This sword has 5 charges and regains 1d4 + 1 expended charges daily at dawn. You can choose to expend 1 of the sword's charges when you hit a creature with it. When you do, the crystalline light flashes, and the target of the attack must make a DC 15 Constitution saving throw. On a failed save, the creature takes 2d8 radiant damage and is weakened until the start of your next turn. On a successful save, the creature takes half as much radiant damage and isn't weakened. A weakened creature deals only half damage with weapon attacks that use Strength and has disadvantage on Strength checks.

Alternatively, you can use an action to hold the sword aloft and expend 2 of its charges to intensify its sickening light, doubling the radius of its bright and dim light to 20 feet, instead of 10. Each creature within the bright light, including yourself, must succeed on a DC 13 Constitution saving throw or be weakened until the end of its next turn. You have advantage on this saving throw. The light then returns to normal.

Step into the light, and feel yourself come undone.