Unlockable stage

An unlockable stage is a stage that is not available at the start of the game (unlike a starter stage), but must be unlocked. Just like an unlockable character, it is required to accomplish a particular in-game feat and once completed, a message will tell him/her that the stage is unlocked. In Super Smash Flash, there were only two unlockable stages, which were Battlefield and Final Destination, stages which have appeared in Super Smash Bros. and Super Smash Bros. Melee as unlockable stages and in Super Smash Bros. Brawl as starter stages.

In Super Smash Flash 2
Any information unlockable is unknown.

Trivia
In demo v0.7, the stage Chaos Shrine was revealed as an unlockable stages, however, for following demo releases, Chaos Shrine is shown permanently as a starter stage.