Super Smash Bros. Brawl/Unlockables

Secret Characters
Complete one of the objectives for each character, not all 3 are necessary. All characters can also be unlocked in the Subspace Emmisary.

Ness

 * Play 5 matches in Brawl mode, then defeat him in battle.
 * Reflect ten projectiles, then defeat him in battle.
 * Complete Stage 29 of the Subspace Emissary and Ness will join your party.

Marth

 * Play 10 matches in Brawl mode, then defeat him in battle.
 * Finish Classic mode on any difficulty level, then defeat him in battle.
 * Complete Stage 8 of the Subspace Emissary and Marth will join your party.

Luigi

 * Play 22 matches in Brawl mode, then defeat him in battle.
 * Beat Classic on any difficulty with no continues, then defeat him in battle.
 * Complete Stage 29 of the Subspace Emissary and Luigi will join your party.

Falco

 * Play 50 matches in Brawl mode, then defeat him in battle.
 * Beat 100-Man Brawl, then defeat him in battle.
 * Complete Stage 18 of the Subspace Emissary and Falco will join your party.

Captain Falcon

 * Play 70 matches in Brawl mode, then defeat him in battle.
 * Beat Classic Mode in under 12 minutes on at least Normal difficulty, then defeat him in battle.
 * Complete Stage 20 of the Subspace Emissary and Captain Falcon will join your party.

Lucario

 * Play 100 matches in Brawl mode, then defeat him in battle.
 * Beat all 5 difficulties on Target Smash, then defeat him in battle.
 * Complete Stage 21 of the Subspace Emissary and Lucario will join your party.

Snake

 * Play 130 matches in Brawl mode, then defeat him in battle.
 * Play 15 matches on Shadow Moses Island stage, then defeat him in battle.
 * Complete Stage 23 of the Subspace Emissary and Solid Snake will join your party.

R.O.B.

 * Play 160 matches in Brawl mode, then defeat him in battle.
 * Collect 250 trophies, then defeat him in battle.
 * Complete Stage 27 of the Subspace Emissary and R.O.B. will join your party.

Ganondorf

 * Play 200 matches in Brawl mode, then defeat him in battle.
 * Beat Classic Mode on Hard difficulty with Link or Zelda, then defeat him in battle.
 * Rescue Link and Zelda in Stage 30 of the Subspace Emissary, complete the stage, and Ganondorf will join your party.

Mr. Game & Watch

 * Play 250 matches in Brawl mode, then defeat him in battle.
 * Beat Target Smash with 30 characters on any one difficulty level, then defeat him in battle.
 * Mr. Game & Watch will join you when you defeat the boss Duon in part 25 of the Subspace Emissary.

Sonic

 * Play 300 matches in Brawl mode, then defeat him in battle.
 * Beat Classic Mode on any difficulty with 10 characters, then defeat him in battle.
 * Play over 10 hours in Brawl mode.
 * Complete Stage 31 of the Subspace Emissary, and Sonic will join your party.

Jigglypuff

 * Play 350 matches in Brawl mode, then beat her in a match.
 * Complete the Subspace Emissary, then return to Stage 18. At the end of the level where you must shoot yourself through barrels, stop on the platform below the new door. Go in and beat Jigglypuff.
 * Complete 20 or more single-player Events after beating the Subspace Emissary.

Toon Link

 * Play 400 matches in Brawl mode, then defeat him in battle.
 * After completing Subspace Emissary, finish Classic mode with any character on any difficulty, then defeat him in battle.
 * Complete the Subspace Emissary, then return to Stage 9. At the beginning of the level after the first mini-battle with Primids, a new door appears. Go in and beat Toon Link, then finish the stage.

Wolf

 * Play 450 matches in Brawl mode, then defeat him in battle.
 * Beat Boss Battles mode with Fox or Falco, then defeat him in battle.
 * Complete the Subspace Emissary, then return to Stage 14. At the end of the second part of the level, go to the bottom of the elevator shaft instead of going into the door and into the new door that appears there. Beat Wolf, then finish the stage.

Music
Information about unlockable music can be found here.