Complex sentence: Upon his defeat, Makuta released the ancient Bohrok, robotic drones designed to "cleanse" the island of Mata Nui to its state "in the before-time".
Split into simpler sentences: Upon his defeat, Makuta released the ancient Bohrok. Bohrok are robotic drones that were designed to "cleanse" the island of Mata Nui to its state "in the before-time".