This cursed item type is indistinguishable from a normal crystal ball, and it radiates magic, but not Evil, if detected for. 

Any magic-user attempting to use it will become hypnotized, and a telepathic suggestion will be implanted in his or her mind. 

The user of the device will believe that the desired object was viewed, but actually he or she became partially under the influence of a powerful magic-user, lich, or even some power/being from another plane. 

Each further use will bring the crystal ball gazer more under the influence of the creature, either as a servant, tool, or possession object. 

As referee, you must decide whether to make this a gradual or sudden affair according to the surroundings and circumstances peculiar to the finding of the crystal hypnosis ball and the character(s) locating it.