At the title screen, press Left, Right, X, B, A, Y, RB, RT, Down, Up, LB, and LT in that order. If done correctly, you'll get a confirmation that everything in the game has been unlocked, though save data, achievements, and posting to leaderboards will be disabled until you restart the game from the Xbox Dashboard.
Left, Right, X, B, A, Y, RB, RT, Down, Up, LB, LT - Unlock Everything
the IDEAL (10) Spring Valley cleared.
the POSSIBILITY (20) Mystic Forest cleared.
the CONFUSION (30) Soft Museum cleared.
the AFFECTION (10) Splash Garden cleared.
the CONSCIOUSNESS (20) Frozen Bell cleared.
the REVIVAL 30 Stick Canyon cleared.
the GROWTH (40) Twin Seeds cleared.
into dreams... (50) Cleared all stages with All A Rank.
DREAMY !!! (30) Got best rating "DREAMY" in Acrobat Time.
Paraloop Master (100) Successfully Paralooped all of Gillwing’s tail in one hit.
Mystic Garage (10) Guided the lost car to the garage.
Hello Mepian (40) Witnessed the hatching of Mepian.
Merry Christmas! (10) Spring Valley (Christmas) cleared.