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)

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)