It's not out yet.
beat story mode
In Super Smash Flash, clear Classic Mode with the 13 original characters to unlock Mr. Incredible.
clear adventure mode
In Super Smash Flash, unlock Young Link by completing Classic Mode on any difficulty with Link.
keep beating everyone and then you should unlock it
To unlock Naruto in Super Smash Flash complete adventure mode with the original 13 characters.
The Battlefield stage is accessible in Super Smash Flash after you clear All-Star Mode as any character.
To unlock Zero in Super Smash Flash, you have to beat Adventure Mode on at least Normal Difficulty without getting a Game Over as Megaman.
Jigglypuff - Clear Event Mode.
beat adventure mode with everyone
Complete tails in Classic mode and Knuckles in Adventure mode and Classic mode.
One way to unlock Luigi in Super Smash Flash is to clear Adventure Mode with Mario on Normal Difficulty or higher. Another way could be hacking.