Play as King of Fighters '94 Kyo Kusanagi

Highlight Kyo, hold START, then press any button.

Play as Orochi Iori

At the Character Select screen, hold START and move joystick Left, Right (at least 4 times) then press A + C together.

Play as Orochi Leona

At the Character Select screen, hold START and move joystick Up, Down (at least 4 times) then

press B + D together.

Play as Orochi New Team

Enter the Orochi Leona code, then return to the character section screen, hold START and move joystick Up, Left, Down, Right, Up, Down then press B + C together.

Play as Orochi characters (PSX)

Press L1 + R1 to access all Orochi characters.

Play as King of Fighters '94 Kyo Kusanagi (PSX)

Highlight Kyo, hold START, then press circle.

Play as Orochi (PSX)

Enable the "Orochi Characters" code, then press L2 + R2 to access Orochi.

Orochi himself is only playable in practice/versus mode.