Complete at least one song with a 'platinum' rank in each venue in Showtime mode to unlock the 'Cheat Collection 1' option. Then, select the 'Cheats' option at the 'Extras Menu', select 'Cheat Collection 1', then enter one of the following codes to unlock the corresponding cheat option. A sound will confirm correct code entry.

Big Eyed Character Press Circle(2), Square(2), Down, Left, Left, Down.
Banana microphone: Press Down, Up, Left, Right, Square, Circle, Square, Circle.
Toothbrush microphone: Press L2(2), Square, Circle, Down, Up, Left, L3.
Dwanye doll microphone: Press Square(2), R3, Circle, Up, Down, Right, Left.