To fight Oboro Bishamon and get the special ending, you need to defeat each opponent without losing a single round and using a specific EX Finisher . The specific EX Finisher required is noted below. After beating the last boss, Oboro Bishamon will appear. You'll get the special ending after the credits.

When fighting as Felicia, go up to your opponent and press the 1P/2P button. Instead of doing her normal taunt, she'll cling onto the other character and say something before letting go.

She can also jump onto the opponent's head, and if no one moves, she will continue to sit there.

-Extra battle-
If you make 3 EX FINISH without losing a round, a character will challenge you. It will be harder than the typical computer player.

-Soul Mode-
On the character select screen, go to the random select box, press Start 5 times, then push any punch or kick button.

-Alternate Soul Mode-
On the character select screen, go to the character whom you would like to use first stage, press Start 3 times, then go to the random select box, press Start 5 times, then push any punch or kick button.

-Dark Talbain/Dark Gallon-
On the character select screen, go to J.Talbain/Gallon, press start and all 3 punches simultaneously. The timing has to be exact.