At least half of them will be filler characters for team battles. For example, I'm pitting Doctor Who vs Rick Sanchez.
This makes the total amount of fighters 64.
Other filler characters include:
Bowser
Ridley
SMBZ Mecha Sonic
Ultron
Dan Hibiki
Magikarp
Freiza
Cell
Kratos
Iron Man
Samurai Jack
Sephiroth
Black Mage
Asura (Asura's Wrath)
Solid Snake
Raiden (Metal Gear)
Fulgore