Conquerors of the Future - S3.E22

The Legion of Doom has suddenly started acting heroic, much to the shocking surprise of the Super Friends. When a distress signal is transmitted to the Justice League computer, the Legion of Doom (acting as the Legion of Good) offers to help instead, but this proves to be a ruse in order for them to travel in time to the year AD 3984 to finally conquer Earth, aided by a savage group of futuristic mutants. With the Riddler leaving cryptic clues easily broken by Batman, the Super Friends learn in a much further century about their takeover and travel to 3984 to foil them.