Unlockable character

An unlockable character is a character in the Super Smash Flash series that is not available at the start of the game (unlike a starter character), but must be unlocked. Unique criteria must be met in order to unlock a certain character. In both Super Smash Flash and Super Smash Flash 2, typically, the player must accomplish a particular in-game feat and once complete, a message will display: "Warning! Challenger Approaching!" with a white question mark block over the black silhouette of the mystery character that it is about to face. By winning the challenge and defeating the opponent, the character becomes playable. In it will be the same although the tasks the player must complete to unlock the characters are still unknown.

In Super Smash Flash 2
It is confirmed that all characters added after the initial release of Beta v1.0.0 will be unlockable in the full version of SSF2.

In demos
These three characters were unlockable in early demos for the sake of their initial inclusion in SSF2.

Trivia

 * In the original "Challenger Approaching!" screen for SSF2, the silhouette of the McLeodGaming's fist logo can be seen.