In
NetHack, a
crystal ball is very heavy to carry around and not particularly useful. Its principal value is the humorous messages it produces if you attempt to use it while
hallucinating. Crystal balls are generated with 1 to 5 charges; they can be recharged to six charges with a
scroll of charging.
If the ball is not cursed, using it allows you to search for an object or symbol, with the chance of success equal to your Intelligence / 20. If it fails, you suffer effects as if the ball were cursed.
A cursed crystal ball will do nothing, blind you, cause you to hallucinate, confuse you, or explode in your face. A potion of object detection or a cursed scroll of gold detection is a much safer way to find stuff.