In order for the greatest weapon in the game to become invisible (the Great Fairy Sword or GFS), you will need the GFS (duh) and the Postman's Hat. Wear the hat, and have the GFS equipped to an item button (anywhere on the c-stick, doesnt matter which one) and have it out. walk up to a postbox, and when it asks for a letter, tilt the stick (or press the X, Y, Z button to correspond to it) in the direction of the GFS. the mailbox will refuse it, and when you regain control of Link, the sword will be invisible. Links hands will appear to hold nothing, but swing the sword and an air swipe will appear. the invisible sword will only last for that section of clock town you are in until you leave to go to termina field or another area in clock town.