VGFacts

To get the Door of Time open, the game actually only needs you to know/play the Song of Time at the Pedestal. 

(BTW, this was pictured and tested by me, if someone else tested what I'm talking about (which I know someone tested the latter portion) I take no credit for finding this out, I simply did this specific test.)
This is the Debug Menu in V. 1.0 of Ocarina of Time. This menu can allow you to edit many things about Link's inventory, but the two items highlighted (below the top most one) are the most important. The higher of the two "Seals", is where you can set which Medallions you have (in order, Forest, Fire, Water, Spirit, Shadow, and Light) and the bottom one, "Ocarina", sets which Ocarina songs you have, allowing you get them earlier than you should. Using this, it is possible to get the Door of Time open without even getting the Spiritual Stones.

(Note the Fairy Ocarina)


This is because the game's flags run on a lot of assumptions.
For example, I was originally testing this on actual Gamecube copy of Ocarina of Time rather than an emulator. My original hunch was that the game only checked for the second-two Spiritual Stones. Not surprisingly the game told me I had all three, even when I only had two. What is even weirder is that in order to get the Ocarina of Time itself, the game checks for all 3 stones before playing the cutscene in which Ganon gives chase to Zelda on horseback.
Back to the Door of Time, when I  knew and played the Song of Time, the game assumed two things:

- I had the Ocarina of Time
- I had the three spiritual stones

This is because the game assumes in order to have played the Song of Time, I must've triggered the cutscene in which you get the Ocarina of Time, and in order to do that, I must've gotten the three spiritual stones, so when I play the Song of Time, the game doesn't check for any of them, assuming I got them.

These assumptions can actually cause a really funny (read: annoying) glitch. I gave myself every single Ocarina song including the warp songs. If you play the Prelude of Light after getting the Fairy Ocarina, the 3 stones will be resting on the pedestal, as if the Door of Time was opened. If you actually play the Song of Time to open the door, the three stones will layer on top of each other, move to the center of the pedestal, and the door won't open. It's not a graphical thing either, the door's collision data is still there. It just doesn't open.


So with the door open, I'm freely allowed to become Adult Link (read: Samus. It's a model swap mod.) So I did.

I had heard that the game only checks for the Shadow and Spirit Medallions in order to trigger the Light Arrow cutscene. This is true. Heck, I even outright removed the Light Medallion from my inventory, and cutscene played just like normal, and I obtained the Light Arrows.


 Because of this, I can also trigger the custcene that creates the bridge to Ganon's Tower, and go inside.




This is going to need some explaining. The reason the game only checks for the Spirit And Shadow Medallions is similar to the Spiritual Stones thing I talked about earlier; The game's flags run on a lot of assumptions.
If you have the Shadow and Spirit Medallions the game assumes 3 things:

- You have the Light Medallion
- You've gotten the Forest, Fire, and Water Medallions
- You've triggered the Shadow Temple cutscene in Kakariko Village (in which the village is on fire)

The reason the game assumes all these things is simple.
1: You're Adult Link, so forcibly go the Light Medallion, no need to check for it.
2: In order to have gotten the Shadow Medallion, the game assumes you must've gotten the Forest, Fire, and Water Medallions, as you need them in order to trigger the cutscene in which you learn the Nocturne of Shadow, the only way of getting into the Shadow Temple.
3: Since the only medallion that isn't reliant on something else is the Spirit Medallion, the game also checks for it.

What is a bit odd, is that in order to trigger the bridge cutscene, the game once again checks for the two medallions along with the Light Arrows, instead of just the Light Arrows.


Well, I think that is everything I wanted to say. If you actually read through all of this, congrats.

Step 1: Complete.
Step 2: Getting this into an abridged version of the intros so it can be submitted.