Fight as Geese:
Complete level 40 in the time attack challenge. Then, hold R while choosing Billy at the character selection screen.

Fight as Goenitz:
Complete level 30 in the time attack challenge. Then, hold R while choosing Rugal at the character selection screen.

Fight as King:
Complete the single attack challenge.

Fight as Kusanagi:
Hold R while choosing Kyo at the character selection screen.

Fight as Orochi Chris:
Hold R while choosing Chris at the character selection screen.

Fight as Orochi Iori:
Complete level 20 in the time attack challenge. Then, hold R while choosing Iori at the character selection screen.

Fight as Orochi Shermie:
Hold R while choosing Shermie at the character selection screen.

Fight as Orochi Yashiro:
Hold R while choosing Yashiro at the character selection screen.

Fight as Shingo:
Complete the team attack challenge.

Random character select:
Hold R2 at the character selection screen.