The Fierce Deity

Truth is...

When you think about it, does the Fierce Deity not look like Adult Link? Ocarina of Time, or Twilight Princess maybe? He does. So maybe it's Link's spirit. Wait, but Link's not dead and not an adult. Okay, so where does that get us? Well, remember that I said that the Happy Mask Salesman said it was a special mask, that it held power greater than Majora? Also, Majora mentioned that the "Game of Tag" was between "Good and Evil"? Hmm, maybe we're onto something here.

I believe that it is possible that this deity is actually Link from another time period. Perhaps Skyward Sword, or another hero that has yet to be mentioned. Or maybe one from a different timeline. Let me explain why.

Here it is, plain and simple: the Fierce Deity Mask is a spirit of Link that gained too much power and lost control. How, you ask? The Tetraforce(see above). This is mentioned all the time in LoZ theories. We know the Triforce, and we know it has a hollow center. What if that hollow center is actually a missing piece, never found or even mentioned in the games thus far. Still, it's possible that this "Link Spirit" went mad when he finds the missing piece, which is why he's considered evil. Ganondorf went crazy when he just had one, the piece of Power. Even though Link has a strong constitution, quadrupling that power would make anyone go crazy. This also explains why he's so powerful. He's got all the powers of the Goddesses at his disposal.