Characters:
(I decided to change this a bit. Here's the Legend:
SW - This is the special way to unlock the character.
NB - This is the number of brawl matches needed to unlock the character.
SE - This is the place where you'll encounter the character in SSE for the automatic unlock.
Captain FalconSW - Beat Classic on Normal Difficulty under 12 minutes (somewhat like before)
NB - 70
SE - Meet up with Olimar
Falco SW - Beat 100-man melee (just like before)
NB - 50
SE - Meet up with Fox and Diddy
GanondorfSW - Clear Classic on Hard with Link or Zelda (reminiscent of the event match)
NB - 200
SE - Finish Kirby Subspace Level
JigglypuffSW - Complete 20 Event Matches AFTER completing SSE
NB - 350
SE - Play Falco's first level again. After beating the shadow boss, find the portal near all the cannons
LucarioSW - Complete all 5 Target Tests levels with any one character
NB - 100
SE - Reach the summit with Metaknight & Ice Climbers
LuigiSW - Complete Classic Mode without continues
NB - 22 (what's with the number 2...remember how to get him in adventure mode?)
SE - Finish the level where every PC that joined your party teams up and play the next.
MarthSW - Complete Classic with any character on any difficulty (this was Jigglypuff's)
NB - 10
SE - Finish the level where you first see Squirtle and play the next.
Mr. Game & WatchSW - Beat Target Test with 30 different characters
NB - 250
SE - Have PCs team up at the Halberd and beat a robot boss
NessSW - Reflect ten projectiles (Well, at least it's easier)
NB - 5
SE - Same as Luigi
RobotSW - Get 250 trophies
NB - 160
SE - Find the R.O.B. Squad and the Ancient Minister
SnakeSW - Play 15 matches on Shadow Moses Island
NB - 130
SE - Finish the level where Mario and crew help Marth and crew eradicate the primids and crew
SonicSW - Beat Classic with 10 characters (wasn't this Marth's)
NB - 300
SE - Before the Final Boss
Toon Link SW - Beat Classic with Link AFTER completing SSE
NB - 400
SE - Play Link's first level, find the portal after the first flash fight
WolfSW - Complete Boss Battle Mode with Fox
NB - 450
SE - Play the level where you find Ivysaur again. Skip the first door you pass when being lowered in to the pit. Instead enter the second door at the bottom.
Wario (to join party)Grab Wario's Trophy during Kirby's Subspace level.
All-Star ModeGet all HIDDEN CHARACTERS
(OK...so that is the final roster. 35, I'm fine with that)
Boss Battles ModeBeat the SSE
(hmm...obvious)
Since Sakurai made an update on it, I might as well refer you
here for the rest of the unlockables.