The Fierce Deity's Mask is one of five Masks that transform Link when worn, alongside the Deku Mask, the Goron Mask, the Zora Mask, and the Giant's Mask. When worn, it transforms Link into Fierce Deity Link. In this state, Link has an adult form and voice, and attacks with the Fierce Deity Sword which can release Sword Beams at the cost of Magic Power. Link has significantly greater strength and range while in this form. When obtained, it is suggested to be as dangerous as Majora's Mask.

Link can obtain the Fierce Deity's Mask by trading the twenty non-transformation masks to the four children inside the Moon. Since the Deku Mask, Goron Mask, and the Zora Mask cannot be traded, Link must have in his possession all of the other masks before being able to receive the Fierce Deity's Mask. Once this has been done, the young hero obtains the mask from the child wearing Majora's Mask. He gives him the mask so that the two of them can "play" together. It is said to possess the merits of all Masks, as well as the memories of all the people of Termina.