Petrifying Gaze

When a target which can see the creature’s eyes starts its turn within 30 feet of the creature the creature can force the target to make a Constitution saving throw (DC = 8 + proficiency bonus + Constitution modifier) if the creature isn't incapacitated and can see the target. If the saving throw fails by 5 or more the target is instantly petrified. Otherwise on a failed save, the target magically begins to turn to stone and is restrained. It must repeat the saving throw at the end of its next turn. On a success, the effect ends. On a failure, the target is petrified until freed by the greater restoration spell or other magic. A target that isn't surprised can avert its eyes to avoid the saving throw at the start of its turn. If it does so, it can't see the creature until the start of its next turn, when it can avert its eyes again. If it looks at the creature in the meantime, it must immediately make the save. If the creature sees itself on a polished surface within 30 feet of it and in an area of bright light the creature is, due to its curse, affected by its own gaze. (Medusa, pp. 214, MM)