Here is my theory about the FD mask. and Majoras mask. Majora was created to punnish termina for what it had done by the goddesses. but the FD came and destroyed majora sealing her power in a mask and sending it to the desert place. but majora got back at him and sealed his powers in a mask too. the Fierce diety saved termina and then when majoras mask escaped it was doing its job. but before its return the goddesses got their revenge. but majora still completed its job. when the kid with majoras mask on said that he was the good guy thats what he thought to be true. and he gave you the mask of the FD "the bad guy". but the goddesses sealed a part of the triforces power in it. So majora thought that he was doing good. and so did link and the FD. and then all is well in termina in the end.