First, move the cursor in a shop above or below the item you wish to buy - whichever item you hover over preferably should have a cheaper cost than the item desired. Then press Up or Down on the D-Pad (towards the desired item) and the A Button at exactly the same time - you should buy the item you wanted, at the cost of the item you hovered over!
Press and hold A and B on Controller 1, then turn the console off and on again. After, during gameplay, access the status screen via Start and press A on Controller 2. This enables very quick movement. Press any D-Pad button for invulnerability, all items, all equipment, and max (255) MP as well.
First, you must equip a sword that can charge to the second level, as well as the ball to go along with it. Hit Select and bring up the menu again, then swap to a sword that cannot charge to the second level. Keep the menu up and save the game, then reset - the newly-equipped sword will then be able to charge to the second level!
To pause the game, press B on the second controller.