Complex sentence: While searching for Woody, Buzz is imprisoned by Utility Belt Buzz, who believes that Buzz is a rogue space ranger; he joins the other toys, who mistake him for Andy's Buzz.
Split into simpler sentences: While searching for Woody, Buzz is imprisoned by Utility Belt Buzz, who believes that Buzz is a rogue space ranger. The new Buzz joins the other toys, who mistake him for Andy's Buzz.