Spoiler Demise and the Sealing Spike

[Sage of Time]

First of all, I don't think Impa or Hylia put the Spike there in the first sealing. I think it was placed there by the three golden goddesses because of the symbols. The spike is triangular shaped, and on each side there was a symbol from each of the three realms visited in the game. One was Din's symbol, one was Farore's, and one was Nayru's. What I think is that Hylia had just defeated Demise, sealing him under the ground with her own power. Soon after, she needed the added power of the golden goddesses, so they used that power to create the Sealing Spike, making the seal stronger. One other part of the game that suggests that the seal can adapt and change is the symbol you draw after each battle with the Imprisoned. The first time, you draw one triangle, then two, and then three, and the sealing symbol on the ground changes accordingly. I don't know if this is coincidence or if Ghirahim chose where in time to travel, but either way he ended up in just the right time to break Demise's seal, when it only was enforced by Hylia's power.
That's my theory on the Sealing Spike

Edit: I's like to add one more point that I find interesting. It involves the one, two, and three triangle symbols I mentionted earlier.
First Imprisoned battle= Skyward Sword=one triangle
Second battle=Master Sword= two triangles
Third battle= True Master Sword= three triangles
Perhaps this has something to do with this: The skyward sword contains Hylia's powers alone, The Master Sword adds the golden goddess's powers, and the true Master Sword adds an extra "dose" of Hylia's power.
This would parallel my Sealing Spike theory.
First sealing=Hylia's symbol (on the ground)= Hylia's power
Second sealing= sealing spike= golden goddess's power
Third sealing group (during SS)= Link+Triforce= extra "layer" of Hylia's power.
I thought this seemed like an interesting pattern.

 

[SuperMetroid]

There's a lot that Skyward Sword didn't answer. In fact, if it was supposed to be a game that answered questions (namely Ganon's and the MS' origins), then it really didn't to a good job of it. For every loose end it answered, there were dozens upon dozens of new questions that could be asked. And don't forget the odd paradox here and there. I'm afraid that any theories one makes about this is going to be little more than fan fiction. Probably the biggest annoyance of anything one tries to discuss about the final battle is the change in locations of Demise's sealed place (changing between the Master Sword and the Sealing Spike). Just thinking about it makes my head hurt. I think Sage of Time is onto something though, in regards to the symbols around the Sealing Spike in the future. I think it'd be worth noting the different markings at each of the different times. Maybe sealing the Imprisoned has more effect on the MS than the Sealing Spike itself. As I've hinted earlier, it's all pretty much loose ends.

 

[felipe970421]

(changing between the Master Sword and the Sealing Spike)

Perhaps they are the same thing?