Unlockable character
An unlockable character is a character 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. Typically, the player must accomplish a particular in-game feat and once complete, a message will display: "Warning! Challenger Approaching!" with a silhouette of the character you are about to face. By winning the challenge and defeating your opponent, the character becomes playable.
Super Smash Bros. Brawl
Masahiro Sakurai once stated that he feels that it would be appropriate that third-party, or "guest" characters, like Solid Snake or Sonic the Hedgehog, would be unlockable. This became true when Super Smash Bros. Brawl came out on January 31.
Also, all unlockable characters can be unlocked by playing through The Subspace Emissary. Once a character joins a group of playable characters, the character will be instantly unlocked for normal play (without requiring a "Challenger Approaching" battle). However, some characters must be battled to before they will join your party.
