Carbunkle
Defeat Carbunkle and successfully complete the Extra Course level to unlock him in Double Puyo Pop.
Satan
Defeat Satan in the G. Dark Prince Castle level to unlock Satan in Double Puyo Pop.
Sound test
Defeat Kaakun two times in the Trial Labyrinth to get Card 18. Enter the options menu and select "Gallery". Choose option 18 to view character artwork. Press [A] to cycle through the game's sounds.