Dymok

Dymok was a planet that was created by the Celestial Toymaker to help him find a replacement host for the Toymaker now that Rallon was dying.

Although the Toymaker attempted to sow discord between the Fifth Doctor and his companions, Adric, Tegan and Nyssa, they rallied themselves in time to help the Dymova disrupt the Toymaker's link with Rallon, allowing Rallon to expel the Toymaker from his body by triggering all twelve of his regenerations at once. The Toymaker was subsequently delayed when Rallon's Watcher merged with the Toymaker to keep him in check in the future. (PROSE: Divided Loyalties)