Cunning Opportunist. The stone cursed has advantage on the attack rolls of opportunity attacks.
False Appearance. If the stone cursed is motionless at the start of combat, it has advantage on its initiative roll. Moreover, if a creature hasn't observed the stone cursed move or act, that creature must succeed on a DC 18 Intelligence (Investigation) check to discern that the stone cursed isn't a statue.
Unusual Nature. The stone cursed doesn't require air, food, drink, or sleep.
Petrifying Claws. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit:12 (2d8 + 3) slashing damage. If the target is a creature, it must succeed on a DC 12 Constitution saving throw, or it begins to turn to stone and is restrained until the end of its next turn, when it must repeat the saving throw. The effect ends if the second save is successful; otherwise the target is petrified for 24 hours.
Stone cursed are spawned through a foul alchemical ritual performed on a Humanoid that has been turned to stone. The ritual, which requires a mixture of basilisk blood and the ashes from the burned feathers of a cockatrice, awakens a dim echo of the petrified victim's spirit, animating the statue and turning it into a useful guardian.