New York - Viacom's (NYSE: VIA) Nickelodeon on Friday announced plans to launch a massively multiplayer online game for its "Avatar: The Last Airbender" series, which is also being developed into a feature film directed by M. Night Shyamalan set for release in July 2010. The beta version of "Avatar: Legends of the Arena," which will be launched in 81 markets in ten languages on Sept. 15, will be unveiled at Comic-Con this weekend.