The Dark Crystal

A thousand years ago on the planet Thra, a magical crystal is cracked, which allows two new races to appear: the malevolent Skeksis, who use the power of the "Dark Crystal" to continually replenish themselves, and the kind wizards called Mystics.

Jen, a young Gelfling taken in by the Mystics after his clan was killed, is told by his Mystic master that he must heal the Crystal, which can only occur if he finds a shard of which is held by the astronomer Aughra. If he fails to do so before the planet's three suns align, then the Skeksis will rule forever. Jen's master then dies. Meanwhile, the Skeksis' leader also dies and a duel ensues between the Skeksis' Chamberlain Skeksil and their General, both of whom desire the throne. The General wins, taking power and exiling the Chamberlain. Learning of Jen's existence, the Skeksis send large crab-like creatures called Garthim to track him.