Some stuff from the few OoT source files we have.

Internally, Spirit Temple is referred to as the "Giant Evil God" dungeon.

Shadow Temple and BotW are conceptually meant to be one dungeon with a child part and an adult part, just like spirit temple is.

Happy Mask Shop is known as the face shop. Bad English on the developer's part, or meant to be meaningful?

Every scene contains a flag that seems to determine whether it should be loaded from the cartridge, or a n64dd disk.

The largest C file we have available is not any of the core engine stuff, it's actually the fishing minigame. They really went all-out when they made that one.

It's a little thing, but rupees are internally just "COIN".

Why do I get the feeling this was a recurring issue?

This is already known, but hilarious. Here's how they check Link's age:

First, there's a flag in the save context. (0=adult,1=child).
Then, there's a macro that converts this into age in years (adult=17,child=5)
Then, there's two more macros that convert this BACK into flags.

The Goron's Bracelet is internally the "Copper Bracelet", which goes far better with the progression to Silver and Gold Gauntlets.

Originally, there were a lot more than 3 elemental arrows (this was also known already, but I'm not sure whether we knew all their names).

There it is again

Possibly the most baffling design decision for OoT was the large space of global variables with no name - They just go by SREG(0), SREG(1), etc. in the source code. Then they have a separate text document that states what those variables are currently being used for, if anything.

A lot of them seem to be debug toggles, but there's game logic in the final game driven by them, too. And debug tools that work on them and nothing else: https://tcrf.net/Proto:The_Legend_of_Zelda:_Ocarina_of_Time_Master_Quest/Memory_Editor
I don't know what to make of them, honestly.

Turns out Nintendo was using the SZS file extension for Yaz0 compressed files all the way back in the 90s. I don't think this was documented until the Wii era.

Here's an example of Zelda64 code being reused in Animal Crossing.

You can see the same "load scene from N64DD disk" flag that I mentioned earlier, and an enum inherited from Zelda that says whether a scene is a dungeon or not. But in AC, the enum only has one possible value!

Searched the Animal Crossing source for any other mentions of Zelda. Apparently, they kept the unused spinning triforce animation from Ocarina of Time:

Big find pointed out to me. In Link's code, it lists the 3 normal boots, as well as Link's indoor and underwater walking speed (which are considered to be separate boots).

And then, commented out, an item that was totally removed from the game: DASH BOOTS! (Pegasus Boots?)

Took a quick glance around to see if there was any other commented out code that jumped out as interesting. There was one thing, the fishing minigame apparently contains dummied-out sound test functionality:

More traces of the elemental arrows and Medallion spells. Based on checking a few other places, it looks like Wind==Forest==Twistar, Dark==Shadow, Soul==Spirit. Except Nayru's Love is considered Soul Magic instead of Water/Ice magic.

According to testing done in the final game, Shadow/Wind/Spirit arrows behave like fire arrows, and Ice/Light/Shadow spells behave like Din's Fire and crash.

The src actually contains files for the unused Arrows and spells, but they're 0 bytes and there's no compiled .o files :(

In short, we got hard proof there was meant to be an elemental arrow and a magic spell for each adult dungeon, but neither the final game nor the leaks give us information on what the remaining 3 were supposed to do.

Oh, actually, the damage charts contain entries for four out of six magic spells - only Forest/Wind (Farore's Wind) and Spirit/Soul (Nayru's Love) are missing.

Seems that the other four were all meant to be offensive spells, but they cut things down and kept only Din's Fire.

Sorry, I was wrong.
Din's Fire = Fire Magic = Fire Medallion
Farore's Wind = Wind Magic = Wind/Forest Medallion
Nayru's Love = Dark Magic = Dark/Shadow Medallion

Going by the code, Ice Magic and Light Magic were both offensive, but not Soul Magic. I'm very curious what it did.

@JoeSchmoe0815 asked whether the code for spawning Arwings from chests is there, and it is! (En_Clear_Tag==Arwing)
Not much in the way of explanation though. And this is the only Arwing-related code that wasn't in a missing file.

!!! There's actually leftover assets for prototype versions of Ice Magic, Fire Magic, and Wind Magic!

All three create a vertical column, although only wind magic kept this in the final game. And for some reason fire magic is blue. https://twitter.com/punk_7890/status/1287977494969118720

There's a commented out file with the intruiging name of "DD Message" (Ura/Master Quest text). But on opening it up, it seems all the hint text is just replaced... with this.

@JoeSchmoe0815 asked about why saving and reloading in Link's house as adult doesn't take you back to Temple of Time. Turns out, it was a buggy check that was only supposed to trigger when starting a new file!

Posting this here in case someone only follows this thread: https://twitter.com/MrCheeze_/status/1288996794068807682

Pocket Egg = Handy Cock

Belated correction: N_Coin has nothing all to do with rupees - it's actually the name for Gold Skulltula Tokens, which originally looked like this.

During development, the default filename (used in debug mode and on the title screen) Wasn't Link, it was (as far as we can tell):
だいしぇんしぇい

No clue if there's any meaning to that.

That's very likely it, thanks! https://twitter.com/p0000ls/status/1289291055448207360

During development, the A and B button seem to have had opposite roles. Some of the code still reflects this.

Oh!! Here's something VERY interesting.

The icons for the six medallions here are internally named "h_24_seal_1-6"... but sitting leftover in another folder is another image, "h_32_seal_7".

Open it up and you get... a Triforce that fits perfectly on the Quest Status screen!

Looking at the details, this seems to be a totally unique texture, with more of a glint to it then what the final game shows on this screen.

Sadly, the image is stored in greyscale to save space (heart piece icons are too), so we don't know quite what it looked like originally.

The name itself is very suggestive though, makes you imagine that the screen was originally designed with the idea that it was the reward for saving Zelda, analogously to the medallions... or maybe not. Anyway, here's a lossless version.
https://cdn.discordapp.com/attachments/737559416014110740/743274118471745596/h_32_seal_7.png

To be clear, all we know for sure is that the asset exists, and what its filename is. Here's a more skeptical take on its meaning. https://twitter.com/MrCheeze_/status/1293747368714809345

I decided to look into unused bytes in the save format.

Apparently, along with the Great Fairy upgrades for double magic and defense, there used to be an upgrade for quicker sword attacks!

(And going by the variable names, it seems single magic wasn't a fairy upgrade at first.)

...the unused fields can't all be winners, though. (The comment says "it's free")

It's been known for years that Dark Link has the highly misleading internal name of "Torch2".

Looks like when they removed this torch and added a new actor with the same ID number, they decided it would be less work to rename it to the name of the old actor.

I was curious how much code there was in various first-party games. Thanks to some precompiled ELF files available, we can actually measure this exactly.

Here's a comparison between SM64, Mario Kart, OoT, MM, and Animal Forest (units in bytes).

JacePlace made another huge find: The zelda_tool_scene folder contains early versions of many cutscenes.

There's a ton to look through there, something I just found is that the old Light Arrow cutscene is identical, except for which textbox displays here:

Note, some of these early cutscenes are not designed for the final game's text list. See the early Prelude of Light cutscene below:

Looks like Zelda giving the Light Medallion above was not a glitch - this early version of Rauru's cutscene has him not give you the medallion!

Hey, who moved the well?

Navi's flight used to end slightly differently. Did she hurt her wings?

One of JacePlace's finds. The old song-learning cutscenes have Link do this pose. (There should be a musical note item above his head, but the object isn't loaded in the final scene.)

Apparently, the ground was lowered by a few centimetres after the original version of this cutscene was made?

One of the biggest beta-cutscene discoveries is the Temple of Time touchdown. This one reflects a big part of the game structure that ended up being removed entirely. Take a look:

This and 100 other clues show us that the game used to be structured like this:

When you first become adult, you spawn on the Prelude of Light pad. You see that over the seven years, the Spiritual Stones have lost their luster, and the door of time has closed.

You're stranded as adult until you beat the first three temples, the ones Sheik guides you to. Each one plays a cutscene of the respective stone being restored. Only once you restore all three, you unlock part 3 of game and the ability to travel in time at will.

This is just in time, of course, for the dungeons that have both adult and child parts to them: Spirit and Shadow.

(Special shoutouts to @glitterberri , who translated and gathered a bunch of info on this old cutscene and mechanic. https://www.glitterberri.com/gallery/thumbnails.php?album=13&page=3 )

Here's the other end of this, there are unused cutscenes (even in the final game) to show the restoration of each stone.

After the first two are restored, you get booted back to Meadow/DMC/Hylia. But the final one plays another unused cutscene:

Just realized Spirit/Shadow Temple were designed to have exactly the same structure as each other:

-First, learn a song as adult to unlock the child half of the dungeon (Requiem, Song of Storms).
-Do the child half first (BotW is/was the child half of Shadow Temple).

-Child part ends with a miniboss to unlock an adult-only item (Miyamoto has said that magic was originally exclusive to adult).
-There are two dungeon items, one for each age. The adult one is equipment, and you get it by refighting the very same miniboss as before.