Once you've beaten all the dungeons, wait until the final day when the clock tower opens. Go in there and play the oath to order. You will then see a long cut seen. Once you are on the moon go to the lonely kid with majoras mask thus entering the final battle.
^this is correct, remember you cannot obtain majora's mask at any point in the game, instead you earn the 'Fierce Deities Mask' once you recover all the other masks in the game and trade them to the children on the moon, although you can only use it in boss battles (you get the masks back next cycle) ThatsNotCanon 10:49, March 18, 2012 (UTC
) I dunno. Amazon?
you will find it on a certain skull kid's face.