Sound recorder:
     Press Down + Y at the title screen to record from the microphone.
Press Down + Y at the title screen again to play back the recording.

Bonus gloves:
     Have  the Game Boy Advance games Sonic Advance or Sonic Advance 2
in  the  cartridge  slot  to  unlock  the  pink gloves in Maniac mode.
Alternately, get

     Have the Game Boy Advance game Sonic Battle in the cartridge slot
to  unlock  Amy  Rose's gloves in Maniac mode. Alternately, get 77,777
Heart Points.

     Have  the  Game  Boy Advance game Chu Chu Rocket in the cartridge
slot to unlock the fist gloves in Maniac mode. Alternately, get 88,888
Heart Points.

Sound Test:
     Successfully complete story mode to unlock the "Sound Test" 
option.

Another Story mode:
     Successfully complete story mode to unlock the "Another Story" 
option.

Hair Color option in Maniac mode:
     Find 10 Rabbits.

Studio option in Maniac mode:
     Find 30 Rabbits.

Bull mini-game in Survival mode:
     Complete Scene 8.

Cake Battle mini-game in two player mode:
     Complete the Snowball Fight mini-game in story mode against 
the girl.

Eye mini-game in two player mode:
     Complete the Eye mini-game in story mode.

Swimming On A Tree mini-game in two player mode:
     Complete  the  Swimming On A Tree mini-game in story mode to save
the girl from the crocodiles.

Table Hockey mini-game in multi-player mode:
     Complete the Disk part of story mode.

Seashells mini-game in multi-player mode:
     Complete Scene 16.

Snowball Chase mini-game in multi-player mode:
     Complete Scene 23 in story mode, where you chase the girl.

Skip story mode level:
     Tap the blue button at the lower right corner of the "Start/Quick
Start"  menu  that  appears before a level. Tap the yellow button that
appears.  Tao  the  small button that appears, answer "Yes" to confirm
three  times.  This  can  only be done one time per difficulty setting
during story mode.

Birthday greeting:
     The  girl  will  greet you by saying "Happy Birthday" at the main
menu  on  the  date  that  you  entered as your birthday in the system
settings.

Holiday greetings:
     Set the system date to December 25, January 1, and other holidays
to hear a new greeting from the girl.