Ready 2 Rumble Boxing
  
Game Boy

Play as Kemo Claw: 


  Highlight "Arcade Mode" and press Left, Left, Left, Right, Right, Right, Left, 
  Right, Left, Right.
Play as Nat Daddy: 


  First unlock Kemo Claw, then highlight "Arcade Mode" and press Right, Right, 
  Right, Left, Left, Left, Right, Left, Right, Left. 
Play as Damien Black: 


  First unlock Kemo and Nat, then highlight "Arcade Mode" and press Right, Left, 
  Right, Right, Left, Left, Right, Right, Right, Left, Left, Left.

Thanks to Revolution reader Homie G.!