Fierce Deity Mask

This mask is featured in The Legend of Zelda: Majora's Mask as a bonus. It is rewarded to the player for collecting all the other masks, including ones achieved through sidequests. The mask transforms link into Oni Link. It is commonly believed that the Fierce Deity is some kind of rival of Majora, yet possibly more evil. Much is still unknown about the mask, its origins, or the deity.