Originally released on January 14, 2009, Cartoon Network Universe: FusionFall was a browser-based massively multiplayer online game (MMO). Developed on the Unity Engine by Cartoon Network and Grigon Entertainment, FusionFall was set in the "Cartoon Network Universe", an alternate Earth inhabited by re-imaginings of characters and locations from various Cartoon Network properties. An entirely new character, Lord Fuse, was created to serve as the game's main antagonist, rather than repurposing a preexisting character.
Originally using a subscription-based plan, wherein players who were not subscribed had limited access to in-game activities, FusionFall became entirely free-to-Play on April 16, 2010. On August 23, 2013, it was announced that FusionFall would be shutting down, with servers going offline on the 29th of the same month. Two fan-made attempts to recreate the game, FusionFall Retro and FusionFall Legacy, were begun following the closure, however both ceased development in April 2020, following DMCA requests on the behalf of Cartoon Network.