Can you ulock characters in Super Smash Flash 2 Dojo

If you mean the Super Smash Flash 2 Demo, then yes. By playing 10 Versus matches, at the end of the last one, it will say "New Challenger Approaching!" You fight the Black Mage. If you beat him, then you unlock him and his unique stage. The Super Smash Flash 2 Dojo is just for reference to the demo.