I'd like this information to be archived in one post. I'm not claiming credit for discovery of this or claiming this to be 100% accurate, I'm just pasting what I have read elsewhere. If you have more information or details please let me know.
Here's what I have so far:
Captain Falcon: Beat Classic Mode on Normal
Falco: Encounter in SSE
Jigglypuff: Complete Event match #20
Lucario: Defeat him in Subspace. You must choose Meta Knight as your character for this fight.
Luigi: Beat Classic on Easy
Marth: Beat Classic or play 15 vs matches. (some say you must use Ike in classic, others don't)
Ness: Play 5 multiplayer matches, reflect 10 projectiles, or "convince him to join you" in SSE.
Sonic: Complete Subspace Emissary
Snake: Encounter in SSE or play 10 vs matches on Shadow Moses Island.
Wolf:
To unlock Wolf, go to the stage "iseki" (Ruins). If you can't read Japanese and don't know which stage that is, it's in the eastern mountainous area, and the level has a lot of moving platforms and fire shoots from traps on the ceiling floor very often. Part-way through the level, you'll get to a flat platform that lowers you down a huge pit, and while being lowered down, there are large crystal spikes on the walls that will come out at you... On the way down, you'll see a door, which is likely the one most of us went in because it looks like you fall into a pit if you keep going down. Nevertheless, skip that door, and stay on that platform until it disappears. At the bottom of the pit is another door. Go in that one, and there will be Wolf cutscene.
I need info for Game & Watch, Ganondorf, Toon Link, ROB. Once it's posted I'll add it to this post.
Here's what I have so far:
Captain Falcon: Beat Classic Mode on Normal
Falco: Encounter in SSE
Jigglypuff: Complete Event match #20
Lucario: Defeat him in Subspace. You must choose Meta Knight as your character for this fight.
Luigi: Beat Classic on Easy
Marth: Beat Classic or play 15 vs matches. (some say you must use Ike in classic, others don't)
Ness: Play 5 multiplayer matches, reflect 10 projectiles, or "convince him to join you" in SSE.
Sonic: Complete Subspace Emissary
Snake: Encounter in SSE or play 10 vs matches on Shadow Moses Island.
Wolf:
To unlock Wolf, go to the stage "iseki" (Ruins). If you can't read Japanese and don't know which stage that is, it's in the eastern mountainous area, and the level has a lot of moving platforms and fire shoots from traps on the ceiling floor very often. Part-way through the level, you'll get to a flat platform that lowers you down a huge pit, and while being lowered down, there are large crystal spikes on the walls that will come out at you... On the way down, you'll see a door, which is likely the one most of us went in because it looks like you fall into a pit if you keep going down. Nevertheless, skip that door, and stay on that platform until it disappears. At the bottom of the pit is another door. Go in that one, and there will be Wolf cutscene.
I need info for Game & Watch, Ganondorf, Toon Link, ROB. Once it's posted I'll add it to this post.