This game is also available on Wii.
Note: You will hear a crackling sound if you did it right. This does not work on all enemies (ie bosses).
Ordinarily, you can find any hidden Treasure box at multiple points in the game. The one in Mushroom castle, however, has only 1 oppurtunity, and that is at the beginning of the game. On your first visit to the castle, be sure to jump on Toad's head and ride him to where the door is. You can now jump onto the ledge right above the door and find a Treasure box that can't be found at any other point in the game.