From Zelda Legends Wiki
The stray fairies are a common sight in the dungeons of Termina. The stray fairies are the fragments of a Great Fairy, and if all are united, the great fairy will once more have the power to grant Link some new ability or item. There are fifteen in each of the four dungeons, and one in Clocktown. If the Clocktown fairy is reconstructed during the first three days, the fairy will grant Deku Link the ability to spit bubbles. After the first three days, the Clocktown fairy grants Link the "Great Faiy's Mask," which attracts nearby stray fairies. If the fairy of the Woodfall dungeon fairy is reconstructed, she powers up Link's spin attack. If the Snowhead fairy is reconstructed, she doubles Link's Magic meter. If the Great Bay fairy is reconstructed, she doubles Link's Defensive power. If the Stone Tower fairy is reconstructed, she grants Link the Great Fairy's sword, which is equipped to a C button and is the most powerful weapon in the game.