Clear Arcade mode once on any difficulty setting without losing any Bat Marks. Then highlight Option, hold L and R, and press Start to access the EX Option menu. One of the features allows you to change game language to English. This will change the name of some characters (Bulleta changes to B. B. Hood, for example) and censors the game (all blood is white and the torture chamber stage changes).
In Arcade mode only, highlight the ? box on the character select screen and press L five times. Upon pressing it the fifth time, hold down button L and press any Punch or Kick button. A character is selected at random, but there will be a shadowy figure behind the character named Shadow. Once you win a match this way, Shadow abandons the character, and takes possession of your opponent, so you switch characters for each stage this way.
Vampire Hunter version of Phobos is selectable by highlighting Phobos, holding L, then pressing any Punch or Kick button.
Dark Gallon can be selected by holding L, then pressing any two Punch or Kick buttons simultaneously while highlighting Gallon.
To play as Oboro Bishamon, you must defeat him first. Don't use Auto mode, don't lose any Bat Marks, and finish at least two oppoonents with the listed EX Move shown below. Here's a quick legend, U = Up, D = Down, B = Back, F = Forward, P = Any Punch, K = Any Kick, LP/LK = Light Punch/Light Kick, MP/MK = Medium Punch/Medium Kick, HP/HK = Heavy Punch/Heavy Kick, PP = Any two Punch buttons, KK = Any two Kick buttons:
Pharaoh Salvation (HK, MP, D, MK, HP) or Pharaoh Decoration (HK, MP, LK, D, LP, MK, HP), either is usable in air
Aqua Spread (F, DF, D + PP or KK)
Togakubi Sarashi (D, D + PP), when opponent is knocked down
Beautiful Memory (B, DB, D, DF, F + KK)
Midnight Pleasure (LP, MP, F, MK, MK), at Level 2
Change Immortal (MP, LP, B, LK, MK)
Please Help Me (B, DB, D, DF, F + KK)
Moment Slice (LP, MP, F, LK, MK)
Prova=Di=Servo (B, DB, D, DF, F + K), then press K
Chuukadan (B, DB, D, DF, F + PP)
Gloomy Puppet Show (B, DB, D, DF, F + KK)
Darkness Illusion (LP, LP, F, LK, HP), usable in air
Final Guardian Beta (F, D, DF + KK)
Cosmo Disruption (B, DB, D, DF, F + PP or KK)
+B (B, DB, D, DF, F + KK)
Big Sledge (Rotate two full circles and press KK when close to opponent)
Geldenheim 3 (Rotate two full circles and press KK when close to opponent)
Hell Dunk (F, D, DF + PP)
Once you have done each of these steps, you will face Oboro Bishamon after you defeat Jedah. Make sure you win, you will see your character's ending if you lose, and you will not be able to play as Oboro Bishamon if that happens. Once you defeat Oboro Bishamon, save the game, then enter any game mode, highlight Bishamon, hold L, and press any Punch or Kick button.