Select 'Gallery' at the options menu. Highlight the option to view the intermission sequences, then hold X and press Up, Down, Left, Right.
Alternate title screen
Successfully complete WakuWaku mode in single player mode. Rider will now appear instead of Amitie at the title screen.
Bonus gallery pictures
Have the Game Boy Advance game Puyo Pop Fever in the cartridge slot to unlock bonus pictures in the gallery.
Character select in Single Puyo Pop mode
Select "Single Puyo Pop" at the main menu. Then, highlight a course except for "Free Battle" and press X, Down, Up, A. A sound will confirm correct code entry.
Control Menu Screen
Blow into the microphone at most game menus to move bubbles around.
Get character select in Endless Puyo Pop mode
Select "Endless Puyo Pop" at the main menu. Then, highlight a course and press Up, Down, X, A. A sound will confirm correct code entry. You can now play as any character in classic mode. To have a character's Puyo set, hold X while selecting that character at the selection screen.
Hidden mini-game
Blow into the microphone at the title screen until a number appears at the bottom of the touch screen. Use the stylus or blow into the microphone to keep the falling Puyos from reaching the bottom.
Play as Carbuncle
Play in HaraHara mode. Either get less than four or more than twelve fevers without any continues. Alternately, complete the game with your number of continues as a multiple of 7.