Keaton Mask

You can find Keaton's Mask in both Ocarine of Time and Majora's Mask (Game). In Ocarine of Time you can get it by buying it in The Happy Mask shop after you have give Zeldas letter to the guard. You can then sell it to the guard which you gave Zeldas letter to. In Majora's Mask (Game) you get it by (after 4PM on Day 3)go to The Curiosity Shop Owner in Kafei's place after delivering Anju's letter. Then you can cut the grass in the North Clocktown, and a Keaton will appear and ask you some questions. If you answer them all right, you will get a Piece of Heart.