To unlock GANONDORF:
* Play 200 matches in Brawl, and then beat Ganondorf (from The Legend of Zelda) in a fight.
* Get Ganondorf to join your party in The Subspace Emissary.
* Beat Classic mode on Normal difficulty with Zelda or on Hard difficulty with Link, and then beat Ganondorf in a fight.
To unlock MR. GAME & WATCH:
* Play 250 matches in Brawl, and then beat Mr. Game & Watch in a fight.
* Clear Target Smash with 30 different characters on any single difficulty level, and then beat Mr. Game & Watch in a fight.
* Have Mr. Game & Watch join your party in The Subspace Emissary.
* Clear Classic mode with all characters.
To unlock SONIC:
* Play 300 matches in Brawl, and then beat Sega’s Sonic The Hedgehog in a fight.
* Play over 10 hours in VS mode.
* Beat the Subspace Emissary.
* Clear Classic Mode on any difficulty with 10 selectable characters, and then beat Sonic in a fight.
To unlock JIGGLYPUFF:
* Play 350 matches in Brawl, and then beat Jigglypuff (from Pokemon) in a fight.
* Complete the Subspace Emissary, then beat Classic mode with any character except Ike, and then beat Jigglypuff in a fight.
* Complete the Subspace Emissary, then beat Event Matches #1 to #20, and then beat Jigglypuff in a fight.
* Complete the Subspace Emissary, then return to Stage 18 (The Swamp). On the last part of the level where you are shooting yourself through barrels, stop on the platform below the new door. Go in and beat Jigglypuff in a fight, then finish the stage.
To unlock TOON LINK:
* Play 400 matches in Brawl, and then beat Toon Link (from The Legend of Zelda: The Wind Waker) in a fight.
* Beat Classic Mode on any difficulty (with Link, Zelda or others), and then beat Toon Link in a fight. Can only be done after the Subspace Emissary is completed.
* Complete the Subspace Emissary, then return to Stage 9 (The Forest). On the first portion of the level after the first mini-battle with a few Primids, a new door appears. Go in and beat Toon Link in a fight, then finish the stage.
To unlock WOLF:
* Play 450 matches in Brawl, and then beat Wolf O’Donnell (from Star Fox) in a fight.
* Beat Boss Rush mode (the stadium boss battles in the Subspace Emissary) with Fox (and Falco?), then beat Wolf in a fight. Can only be done after the Subspace Emissary is completed.
* Play as Fox in Stage 14 (The Ruins), which you can find in the eastern mountainous area, it’s a level with lots of moving platforms and fire shoots often from traps on the ceiling. Part-way through the stage (at the end of the second part of the level) a flat platform will lower you down a huge pit, while being lowered skip the first door you pass (don’t worry when the elevator disappears, just fall), instead enter the second door at the bottom that appears there, and then beat Wolf in a fight. If you failed, you can retry this once the Subspace Emissary is completed.
If you don’t unlock ’em all they’ll taunt you forever, like so:
I hope this page is helpful to someone.