These leaks have been getting out of hand recently, so I've gathered a list of every character leaked by the following catalogue of leakers:
Vergeben: Decidedly the most reliable of sources here, Vergeben has an amazing track record for both this game and several others. Among many other things, he announced that Snake and Ice Climbers would return, that there would be no cuts from Smash 4, and that Ridley, Isabelle, and Simon Belmont would be added. Due to his reliability, anything he claimed would be in below is in green.
LaPailleDor (1): A leaker on French forum jeuxvideo, LaPailleDor claimed that Chrom, K Rool, Richter, and Simon would be playable, as well as Dracula as a boss and stage morph being an option, all later coming true. However, the mods of the forum claim that these were faked.
LaPailleDor (2): A 4chan leaker who claims to be LaPailleDor, giving several pieces of evidence of his identity.
WhisslBlank (1): More commonly known as the NeoGAF Leaker, WhisslBlank claimed that K Rool, Simon, and Chrom would be added.
WhisslBlank (2): A second NeoGAF account claiming to be WhisslBlank, offering possibly falsified evidence. As this is likely false, and the claim that Galacta Knight will be a Meta Knight echo is already soft-deconfirmed, anything that only he claimed will be in red.
Ken Leaker: A 4chan leaker who posted an image of Ken in the debug mode. This image has been proven time and time again to be watertight.
Loz18: A GameFAQs leaker who claimed that there would be a Smash direct in August that showed a full tour of the menus, that would show three modes, and that there would be a cutscene themed around heroes vs villains (which turned out to be K Rool's reveal trailer).
Senjougahara Hitagi: A leaker who has got several things right about other games. As Vergeben has backed up Senjougahara and claimed that the two share sources, leaks from them will also be in green.
[4] Ken: Vergeben, Ken Leaker (obviously), LaPailleDor (1), WhisslBlank (1)
[2] Geno: Vergeben, WhisslBlank (1)
[2] Isaac: LaPailleDor (1), WhisslBlank (1)
[2] Skull Kid: LaPailleDor (2), Loz18
[2] Sora: Vergeben, WhisslBlank (1)
[2] Steve: Vergeben, Senjougahara Hitagi
[1] Ayumi Tachibani: LaPailleDor (2)
[1] Bandai Namco Character: WhisslBlank (2)
[1] Black Shadow: LaPailleDor (1)
[1] Dixie Kong: Loz18
[1] Felix: WhisslBlank (2)
[1] Galacta Knight: WhisslBlank (2)
[1] Incineroar: Vergeben
[1] Katalina (or other Granblue Character): Senjougahara Hitagi
[1] Monster Hunter: WhisslBlank (2)
[1] Medusa: LaPailleDor (2)
[1] Ninten: LaPailleDor (2)
[1] Reimu Hakurei: LaPailleDor (2)
[1] Sable Prince: WhisslBlank (2)
[1] Shadow: WhisslBlank (2)
[1] Soren: WhisslBlank (1)
[1] Terra: WhisslBlank (2)
Italicised Names indicates the leaker was not specific about the character, but there is reason to believe they refer to that character.
Not included is the Richter Leak, as the story behind it is extremely unlikely. It claims that Gothitelle and Gardevoir will be playable.