An unlockable character is a character that is not available at the start of the game (unlike a starter character), but must be unlocked. A 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 the player is about to face. The unlockable character will then be fought by the last character Player 1 had used. By winning the challenge and defeating your opponent, the character becomes playable.
Super Smash Bros.
Characters
| Character | How to Unlock |
| Captain Falcon | Beat the single player mode with any character on any difficulty level in less than 20 minutes. |
| Jigglypuff | Beat the single player mode with any character on any difficulty level. |
| Luigi | Complete Bonus 1 (Break the Targets!) with all 8 starting characters. |
| Ness | Complete the single player game on normal difficulty with three stocks and without continuing. |
Super Smash Bros. Melee
Characters
| Character | How to Unlock | VS Matches Required |
| Jigglypuff | Complete Classic or Adventure Mode | 10 |
| Dr. Mario | As Mario, complete Classic or Adventure mode without continuing | 20 |
| Pichu | Complete Event Match #37: Legendary Pokémon | 30 |
| Falco Lombardi | Complete 100-Man Melee | 40 |
| Marth | Play Classic Mode with all 14 starter characters, or use them all in VS. mode | 50 |
| Young Link | Complete Classic Mode with Link after completing Classic Mode with 10 different characters. | 60 |
| Ganondorf | Complete Event Match #29 Triforce Gathering | 70 |
| Mewtwo* | Play VS. mode for a combined total of 20 hours* | 80 |
| Luigi | Complete Stage #1 of Adventure with time ending in a "2" in the seconds meter. After that, beat Luigi and Peach in less than a minute, and then complete the Adventure mode | 90 |
| Roy | As Marth, complete Classic or Adventure mode without continuing | 100 |
| Mr. Game & Watch | Complete Classic, Adventure, or Target Test with all other 24 characters. | 110 |
*The time required to unlock Mewtwo in calculated in "player-hours" (eg. 2 human players gives 2 hours for every hour of game-time, 3 human players give 3, and four players give 4).
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 March, 9, 2008.
Also, all unlockable characters can be unlocked by playing through The Subspace Emissary, some just by playing through, while others involve completing the mode, and returning to specific zones and going through previously absent doors to a playable stage where, after a short cutscene, the player will be able to fight and unlock the character. Jigglypuff, Wolf and Toon Link are unlocked in this way. 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, as per the SSE's story, must be battled to before they will join your party.
Characters
| Character | How to Unlock | Subspace Emissary | VS Matches Required |
| Ness | Reflect 10 Projectiles. | Complete Subspace (Part I) | 5 |
| Marth | Complete Classic Mode. | Complete Battlefield Fortress | 10 |
| Luigi | Complete Classic Mode using no continues. | Complete Subspace (Part I) | 22 |
| Falco | Complete 100-Man Brawl | Complete The Swamp | 50 |
| Captain Falcon | Play through Classic Mode on Normal or higher and beat it in 12 minutes or less. | Complete Outside the Ancient Ruins | 70 |
| Lucario | Clear Target Smash!! on levels 1-5 with any single character. | Complete Glacial Peak | 100 |
| Snake | Play 15 Vs. Matches on Shadow Moses Island. | Complete Battleship Halberd Interior | 130 |
| R.O.B. | Collect 250 different trophies. When done in Coin Launcher, play a brawl also. | Complete Subspace Bomb Factory (Part II) | 160 |
| Ganondorf | Clear Classic on Hard with Link or Zelda. | Collect both Link and Zelda's trophies in Subspace (Part II) | 200 |
| Mr. Game & Watch | Clear Target Smash with 30 different characters on any single difficulty level | Complete Battleship Halberd Bridge | 250 |
| Sonic*** | Complete Classic Mode with 10 characters, or brawl for 10 combined total hours. | Complete The Great Maze | 300 |
| Jigglypuff ** | Beat 20 or more events after beating the Subspace Emissary. (video) | After completing The Great Maze defeat it in a secret room in The Swamp | 350 |
| Toon Link ** | Complete Classic Mode after beating the Subspace Emissary. | After completing The Great Maze defeat him in a secret room in The Forest | 400 |
| Wolf ** | Complete Boss Battles mode with Fox or Falco. | After completing The Great Maze defeat him in a secret room in The Ruins | 450 |
** Toon Link, Jigglypuff and Wolf are not part of the main plot of Subspace Emissary, players must beat the main story first then revisit certain stages to find them that way.
***Sonic is the only character who can be unlocked 4 different ways.