Crystal Ball is an accessory that provides Magic +50. It can be obtained by finding it at Guadosalam during Chapter 5, completing Zu's Fiend Tale, and by getting an Episode Concluded for Moonflow and Mt. Gagazet, by winning it from Chac (Oversoul) or Baralai at the Den of Woe, by bribing Dark Elemental (Oversoul), or as a prize from the Aeon Cup. One Crystal Ball can be consumed to increase any creature's Magic by 1 permanently.
A crystal ball is a crystal or glass ball believed by some people to aid in the performance of clairvoyance. It is sometimes known as a shew stone (or show stone— "shew" is an archaic spelling of "show"). A body of water, either in a container or on the ground, used for this purpose, is called a scrying pool.