The demo version that was just published was an outdated version, full of bugs. The most important ones are a flickering in online mode that makes the matches almost unplayables and a freeze on classic mode, making unable to unlock the 2 secret characters (The antidecompiler we used also influenced this). Our team is working on this and we will fix it as soon as posible, the patch should be up between tomorrow and this monday. Sorry for the inconveniences.
The versus mode works flawlessly, so you can play it meanwhile we upload the patch file. Again, we are deeply sorry for this.