Crystal ball

Crystal balls were used to gain unusual insight.

On one occasion, three Carrionites used a crystal ball to view and possibly influence remote events through a form of verbal science that appeared to 16th century humans as "magical". They were eventually imprisoned within it by the Tenth Doctor, (TV: The Shakespeare Code) who retained the ball within the TARDIS in perpetuity. (TV: The Unicorn and the Wasp)

On another occasion, a fortune teller on Manussa told Tegan Jovanka that she used a crystal ball to pretend to see into the future. Tegan, who was at that time possessed by the Mara, showed her an image of a snake's skull in the crystal ball. (TV: Snakedance)

Morgana used a crystal ball in her fortune-telling act. The Gods of Ragnarok communicated with the Psychic Circus through the ball, and showed them images of their foes' actions. The ball exploded when the Seventh Doctor destroyed the Gods. (TV: The Greatest Show in the Galaxy)

In Germany, the Black Coven used a crystal ball as a telepathic receiver to show the Seventh Doctor that they had captured Ace. (PROSE: Timewyrm: Exodus)