To get all the art work in the game including all ending scenes for every character just beat Goodman in Survivor Play/Mode.

He will be the 21st opponent you'll face.

Once you've beaten Goodman, just lose in the following round or whenever you want in Survivor Play/Mode then exit. You will recieve a notification that you had already unlocked whichever character you had already defeated and is now a playable character in every mode.

To select Mizuchi, Shishioh or Neo-Dio after defeating them in Survivor Play/Mode, simply move your cursor off screen to the far right or left. Your cursor would then disappear and highlight one of the following secret character. Then press up or down to cycle between the 3 characters.

To select Goodman, after defeating him in Survivor Play/Mode and unlocking him, at the character select screen press RIGHT on Yuki or LEFT on Ai and your cursor will disappear and now highlighting Goodman (you cannot see his character select potrait box unlike the other characters not counting Mizuchi, Shishioh and Neo-Dio.

Goodman cannot be teamed up with any character.