In order to test everything coded within the game before the final release, Cleod9 releases to the public, after a certain period of time, the Super Smash Flash 2 Demo, a playable beta version of Super Smash Flash 2. New versions of the demo usually include several new features, new characters or stages, and many bug fixes. The current version of the demo is v0.9.2011.
There is a test demo for exclusive use by SSF2 Devs and SSF2 Balancers called the Developer Demo, or devmo for short. Its main function is to test new content before its public release (and thus preventing bugs from being in the release). Because of its exclusivity, Devs usually enjoy mocking non-devs in the McLeodGaming Forums by showing them screenshots from the devmo, as well spoiling them.
Demo v0.9 has added the most content into the game so far.
Demo v0.8a is the only version to add more characters that appeared in the original Super Smash Bros. game.
Although Super Smash Flash 2 has been in development since 2007, the developers feel that the game didn't truly enter development until 2010 with the release of 0.6.
Demos v0.9a and v0.9b were first shown at Apex 2013 and 2014, respectively, making it the second consecutive year that this happens.
Almost everything that was added to v0.9b were fan-suggested changes to the game, which made the game popularity go far away than before.
Demo v0.9 is the only one so far to use the patch-system capabilities. Because of this multiple versions of v0.9a were made.