Unlockable: Hidden Characters
To unlock the characters below, fulfill the requirement listed. If there is a number in parenthesis next to a character, such as "(160)", this signifies that you can also unlock this character simply by playing that many matches in VS. mode. All characters can be unlocked by meeting them in the Subspace Emissary, as well. Keep in mind that you must defeat the unlocked character in a battle to retain him on the roster permanently.

Captain Falcon - Complete Classic Mode in twelve minutes or less. (70)
Falco - Complete 100-Man Brawl. (50)
Ganondorf - Complete Classic Mode on Hard difficulty using either Zelda or Link. (200)
Jigglypuff - Complete Classic Mode or complete Event Match #20. (350)
Lucario - Using Meta Knight, defeat Lucario in Adventure Mode. Or, complete five Target Tests. (100)
Luigi - Complete Classic Mode on Easy difficulty. (22)
Marth - Complete Classic Mode. (10)
Mr. Game & Watch - Complete Classic Mode with each character. (250)
Ness - Reflect ten projectiles in battle, or defeat him in Adventure Mode. (5)
R.O.B. - (160)
Snake - Play fifteen matches on Shadow Moses Island. (130)
Sonic - Complete Adventure Mode. (300)
Toon Link - Clear Subspace Emissary and then clear classic mode with anyone. You can also find him during Subspace Emissary (after you beat it - in Forest stage). --Jeselle (400)
Wolf - Complete Adventure Mode, and then complete Boss Battle Mode using Fox. (450)