The Legend of Zelda: Majora's Mask/Glitches

Invisible Sword
There are a total of five mailboxes in Clock town. When you walk up to a mailbox, the mailbox will ask you to deposit a letter. You probably won't have a letter on you but if you try to give the mailbox the Great Fairy's Sword, it won't accept it. When the controls goes back to Link you will see Link looking like he is still holding the sword, but alas, it's invisible!

Note that doing this trick may crash the game. The Great Fairy's Sword will go back to normal if you put the sword away, leave, or enter any buildings.

Getting into Sakon's Hideout
This takes many, many tries, but it works! Warp to Ikana Canyon and go to where Sakon's hideout is. Look in the space between the canyon and the right side of the door. Now run and see if you can get through that space in the crack. This takes patience. Once you finally manage to get through to the other side you will find no one there and that you will only find the Suns's Mask (which you cannot get because it takes two people to complete the puzzle.) To get out, you must warp to an owl statue.