Tatl
Tatl (チャット, Chatto; Chat in English) is Link's fairy-companion in Majora's Mask. Along with her purple-colored brother, Tael, her name stems from the term "Tattletale" pertaining to her nature as an informant, particularly of the enemies encountered in the game.
Similar to Navi from Ocarina of Time, Tatl assists Link by allowing him to interact with the environment through Z-Targeting certain objects, people, and enemies. Unlike Navi, however, Tatl expresses herself with bell-like noises of varying repetition, whereas Navi shouts several catch phrases such as "Hey!", "Listen!" or "Watch out!".
In contrast to Navi, Tatl frequently expresses her opinions and partakes an active role in several cut scenes. Initially aggressive and blunt in her treatment of Link, Tatl gradually mollifies as she grows to tolerate his company. Although Tatl provides less information than Navi, the information she does provide is generally more direct, though occasionally vague. When questioned about an enemy from Ocarina of Time, she tends to react with surprise, then criticize Link for his ignorance.
She first encountered the Skull Kid when he was alone in Termina Field, and she and her brother soon made friends with him, accompanying him to the Lost Woods, where they attempted to steal Link's ocarina. However, through a twist of fate, she was separated from the Skull Kid and her brother, and became reliant on Link to help her reunite with (and save) her brother. She would accompany him in his subsequent confrontations with the Skull Kid, and also play a part in preventing Termina from its impending apocalypse.
Tatl and her brother also seem to be well known around Clock Town, at least with the Bombers. After Link receives the Bomber's Notebook from Jim, Jim directly addresses Tatl, telling her to inform the Skull Kid that he is no longer a member of the Bombers. Also, if Link addresses a Bomber as a Goron or a Zora, he asks many questions, such as "Why is Tatl with you?"