Complex sentence: Jareth transports Sarah and himself to the Labyrinth and promises Sarah he will return Toby to her if Sarah solves his Labyrinth and make it to his castle within thirteen hours.
Split into simpler sentences: Jareth transports Sarah and himself to the Labyrinth. He promises Sarah that he will return Toby to her, if Sarah solves his Labyrinth and make it to his castle within thirteen hours.