Location
The Great Fairy Mask is gained by refinding the stray Fairy in Clocktown and returning it to the Great Fairy in North Clocktown. Once you've done that, the Great Fairy can be reformed. The first time you do this, you'll acquire a magical power but the second time you do it, you'll get this mask. The stray fairy will be near the Laundry Pool during the day and at Night it will be in East Clocktown.
Uses
Wearing this mask will help you find the stray fairies in various dungeons. While wearing it, the hair will start to glow if there is a stray fairy nearby. The fairies will normally be drawn to you while wearing this mask but if they are trapped by something, they may not be able to until the obstruction is cleared.
