There are four hidden characters in Super Smash Bros. Here's the criteria to unlock all of them. Assuming you've played along correctly, a "New Challenger!" screen will display, and all the have to do is win against said character to unlock them.
- Captain Falcon - Beat the game with any character, any difficulty, and any number of lives within twenty minutes.
- Jigglypuff - Beat the game with any character, any difficulty, and any number of lives.
- Ness - Beat the game on "Normal" difficulty using only three lives and no continues.
- Luigi - Using all 8 original characters, complete the Break the Targets minigame.