Unlockable refers to any element of the Super Smash Bros. games that is not available from the start, but must be earned by completing some task. A task often requires the player to complete a game mode with a particular character or difficulty level.
For Brawl, there is possibility in theory that some unlockables would be unlockable with memory cards containing Melee data and/or other if the original Super Smash Bros. would be downloadable to the Virtual Console, mostly possibly Past Stage.
Unlockable can refer to: