Complete all songs with a 'Gold' rank in each venue in Showtime mode to unlock the 'Cheat Collection 3' option. Then, select the 'Cheats' option at the 'Extras Menu', select 'Cheat Collection 3', then enter one of the following codes to unlock the corresponding cheat option. A sound will confirm correct code entry.

Small head character: Press Circle, R2, L2, R1, L1, Down(2), Up.
Glass character: Press Down, L2, R1, R2, L1, Circle, Square, Circle.
Oil slick character: Press L3(2), R2, R1, L2, L1, Down, Up.
Ice cream microphone: Press Square, Circle, Square, Circle, R2, L2, R1, L1.