Ruinous Flail

This ash-gray flail is cold to the touch. You gain a +1 bonus to attack and damage rolls made with this magic weapon, and it deals double damage to objects and structures.

Additionally, when you hit a creature with this weapon, you can force the creature to make a DC 15 Constitution saving throw. On a failed save, the creature has the poisoned condition for 1 minute. The poisoned creature takes 2d4 necrotic damage at the start of each of its turns. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Once this property is used in this way, it can't be used again until the next dawn.