All-Night Mask

In Majora's Mask, the All-Night Mask is a mask with the power to prevent its wearer from falling asleep. It was originally a torture device of insomnia, but its creators are unnamed.

Location
Link can purchase this mask from the Curiosity Shop on the night of the final day for 500 Rupees if he protects the Old Lady from Sakon's attack on the night of the first day. If he allows Sakon to steal her bag, the mask will not appear. Interestingly, if shown to the Happy Mask Salesman, he will have nothing positive to say about it, only noting that it looks "expensive."

Uses
While Link needs an entire three day cycle to obtain the mask, it has only one use in the game. If Link wears the mask while listening to the stories of Anju's Grandmother, then he will not fall asleep. At the end of each story, Anju's Grandmother will ask him a simple question. If Link gives the appropriate answer for the first story, The Carnival of Time, he will receive a Piece of Heart (though she calls it "candy"). He will receive another Piece of Heart for answering "I dunno" to the question asked after her second story about the Four Giants.

The Wind Waker
The All-Night Mask appears alongside the Bunny Hood, Goron Mask, and Keaton Mask behind the counter of the Nintendo Gallery. It can be seen hanging on the wall behind Carlov.