Complete all songs without a 'Gold' or 'Platinum' rank in each venue in Showtime mode to unlock the 'Cheat Collection 2' option. Then, select the 'Cheats' option at the 'Extras Menu', select 'Cheat Collection 2', then enter one of the following codes to unlock the corresponding cheat option. A sound will confirm correct code entry.

Big head character: Press Circle, Square, Circle, Square, Up, Right, Down, Left.
Mercury character: Press Down, Down, Right, Left, Right, Left, Square, Circle.
Wraith character: Press L2(2), Right(2), Circle, Square, R1, R1.
Fish microphone: Press Square, Down, Up, Left, Square(2), L2, L1.