So I finally did it. Got all the masks (The Romani/Troupe Leader masks were easy to obtain, and the Truth Mask was kinda tedious) and then did all 4 Moon Child dungeons, which were difficult. I obtained the Fierce Deity Mask, and fought Majora twice. Fighting it normally was tough, and I was near death when I did defeat it; fighting it with the Fierce Deity Mask was easy because it's so powerful.
I'm sure Bloom would be happy to hear all this. You know, if she were still here. Aside from that, I'll be playing Bravely Second now.