While this may be a little lame, here's a new Character Unlock anybody can follow if they want more people to unlock. (Please note - these aren't official, and are just for fun)
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Ness, Falco, Wario, Lucina, Dark Pit, Dr. Mario, R.O.B., Ganondorf, Mr. Game & Watch, Bowser Jr. Duck Hunt, Jigglypuff: Unlock as normal.
OR
Ness: Clear Classic Mode on 5.0 difficulty or higher.
Home Stage: Magicant
Falco: Complete 100-Man Brawl.
Home Stage: Corneria
Wario: Summon Waluigi from an Assist Trophy.
Home Stage: WarioWare
Dark Pit: Defeat Palutena while playing as Pit's purple costume.
Home Stage: Bomb Reset Forest
Lucina: Use Robin's Final Smash while playing in Arena Ferox.
Home Stage: Arena Ferox
Ganondorf: Defeat "Dark Link" while playing as Link.
Home Stage: Gerudo Valley
Mr. Game & Watch: Complete Classic Mode with the original eight starting characters from Super Smash Bros.
Home Stage: FlatZone 2
Duck Hunt: Play "Smash Run" as both R.O.B. and Mr. Game & Watch
Home Stage: Living Room
If you're going to be using the unlock requirements above (for already unlockable characters) remember that they must be unlocked the original way, and then the "custom" way
Captain Falcon: Win in first place at "Race to the Finish!" from Smash Run.
Home Stage: Mute City
Marth: Play Classic Mode with all starting characters, excluding those listed here.
Home Stage: Arena Ferox
Luigi: Defeat Master Hand with a time ending of "2" in the seconds meter.
Home Stage: 3D Land
Toon Link: Complete Classic Mode with Link, Zelda, or Sheik after completing Classic Mode with ten other characters. Reduce to eight other characters if you'd like to go through as Ganondorf.
Home Stage: Spirit Train
Lucario: Win in first place at "300% Smash" with Pikachu, Charizard, or Greninja.
Home Stage: Prism Tower
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Hopefully this will add a bit more variety for anybody who uses it. I'll probably create some more for other characters, too, so I'll update it later. Also, if anybody has any ideas for some of the newcomers, please tell me!