Location
Kafei has this mask in Clock Town and he wears it to conceal his identity. You'll need to perform a delivery side quest with Kafei and once you've completed it, Go to the Curiosity Shop in town after 1pm on the last day to get this mask.
Uses
This mask is primarily used to get a Heart Piece. Wearing this mask in the field, you can try and find Keaton in bushes. If you manage to catch him in the bushes while wearing the mask, he will ask you five questions. If you also successfully answer all five questions, you will get the Heart Piece. Repeating this process on subsequent three day run throughs.
