Boxxle Cheats (GameBoy)

2 D[Spade]XX 
  3 G[Spade]XY 
  4 H[Spade]XZ 
  5 J[Spade]X! 
  6 K[Spade]X? 
  7 L[Spade]X0 
  8 M[Spade]X1 
  9 N[Spade]X2 
  10 P[Spade]X3 
  11 Q[Spade]HT

At the Title screen, hold A + B + Up until the credits appear.