Nickelodeon has announced that as part of the popular show’s continued cross-media expansion, it will launch Avatar: Legends of the Arena in September.

The online multiplayer game was unveiled at Comic-Con on Friday, revealing itself to be a four-player arena combat experience. Young players will also engage with RPG elements, training and dueling in arenas in order to unlock new skills and costumes for their characters. When the game launches in September it will launch globally, opening in 81 territories including the United States, Japan and the United Kingdom. It will be available in ten languages at launch.

“The launch of this multiplayer online game gives Avatar fans the opportunity to immerse themselves in the storylines during and beyond its tenure on-air,” said senior VP of Nick.com Jason Root of the project.

Avatar: The Last Airbender, the show on which Legends of the Arena is based, recently enjoyed its highest ratings ever, with certain shows from the last season garnering up to 19 million viewers. Other upcoming products in the franchise include Avatar: The Last Airbender: Into the Inferno, a fall 2008 game from THQ,  and a July 2010 live action major motion picture directed by M. Night Shyamalan.

The game will be made available at http://www.avatarlegends.com.

Note: Footage from the beta version of the game is pictured.