Nickelodeon is working on a new MMO based on the Avatar: The Last Airbender titled Avatar: Legends of the Arena. The game will serve as a prequel story to the animated series, and will see up to 4 players battling at once inside of 3D arenas. Victories reap rewards, such as new content, challenges, outfits and other unique equipment.
One unique aspect of the game is that you will be able to watch, from September through October, special episodes of Avatar which will give you episode-specific hints for unlocking exclusive game content.
Avatar: Legends of the Arena will be released this September, with a Beta planned to be revealed this afternoon at Comic-Con.