Play as Marionet
At the character selection screen, highlight the "?" icon. Then, press Select(7) followed by any button. Now Marionet will transform into the form of the opponent in each match.

Play as Shadow
At the character selection screen, highlight the "?" icon. Then, press Select(5) followed by any button. Now Shadow will transform into the previous opponent in the next match.

Play as Original Gallon
Beat the game with Gallon. Then highlight Gallon on the character selection screen and press Select + PP or Select + KK.

Play as Hyper Bishamon
Beat the game with Bishamon. Then highlight Bishamon on the character selection screen and press Select + PP or Select + KK.

Play against Hyper Bishamon
Begin a game in single player mode and do not lose in any round and defeat at least two characters with EX moves.

Play as Vampire Hunter Phobos
At the character selection screen, hold Select to choose Phobos.

EX Option, DX Option and the Full Collection
To unlock the DX & EX Option and also the others pictures from collection, you need first to edit a character in the "Original Character" mode. Then you must earn experience with him/her in the 1p Battle. As soon as you earn enough power, life and EX gauge, the new options and pics are going to be unlocked (some pictures come first, then the EX option, more pictures and DX option, in this order).

Easy bonus character select
Enable "Shortcut" mode. Then, highlight the desired hidden character location in shortcut character selection menu. Press Select to turn that character's name red and use that character.