Bone Blight

You inflict a powerful curse on a creature you can see, unless that creature makes a successful Constitution saving throw.

Creatures cursed with bone blight have dangerously brittle bones. They gain vulnerability to bludgeoning and slashing damage, and if they take 20 or more damage from any attack, they must make a successful Constitution saving throw or suffer a broken bone. A broken bone reduces movement to half speed and imposes disadvantage on Dexterity checks. The penalties for a broken bone are removed when the character receives magical healing or finishes a long rest with all of their hit points and hit dice restored.

At the end of each long rest, a character suffering bone blight must make a Constitution saving throw. The curse ends after two successful saves, which need not be consecutive. The curse can also be ended by magic that removes curses.