Major Spoilers for all Expansions - Some general things I didn't understand

[Zero-ELEC]

And also ignore the 'Echo' effect buff given in battles too, that's just again a fancy title given for a leg up for gameplay and has nothing to do with the storyline.

That's not entirely true. We actually do see the "Echo buff" in action not used by us during a story segment, namely, in the solo duty quest battle against the Warriors of Darkness. Once enough of them fall they "call upon the power of the echo" and rise again to fight, with characters noting that it's the power of the Echo that brings them back up and even gain the enhancement "The Echo", like our characters do in duties, becoming stronger.

[Cleretic]

That's just a myth/misconception that just refuses to die like a stubborn Ascian and is quite frankly not true. Fordola doesn't 'read your mind to sense your attacks' before they happen through the Echo, she senses very subtle fibrations through the aether which is why she's so easily incapacitated with Moen's wand thingy blasting a large amount of aether at her, it overloaded her senses and stunned her. Fordola's Resonant power isn't even fully like the Echo (she can't see proper memories as a fully interactive vision for instance, but merely sees fragments of still images like a broken Powerpoint slideshow) - not surprising given it was meant to give magic powers/aether manipulation ability to Garleans (it also was not copied from the WoL either - Krile served as the model for it and she was hardly the most potent in the Echo by her own admission, being more attuned to animals and beasts than being able to read others' memories or understand other languages).

If anything, the fact Fordola's is patterned on Krile's, and Krile's Echo abiliity isn't a world away in description from Fordola's suggests that Fordola got an imperfect and untrained copy of Krile's. Which is an interesting concept; that maybe this is what Krile's teenage years were like, or that the copying process is imperfect enough that it effectively produces something entirely different and much more horrifying.

...Actually, come to think of it, I feel like the one common thread between 'natural' Echo-havers is that their Echo ability is completely worthless for the skillset they actually have. Ours mostly just gives us crippling migraines at inopportune times, Mikoto's gives her actively detrimental amounts of information. Krile probably has it the best, and even she had to work through some rough patches and has now reached the point of being an unrelated element to her skillset that she doesn't think about much.

[Cilia]

snip

I specifically said "unsundered Ascians" and not Ancients for a reason - the memory crystals were made by the three unsundered Ascians (I don't remember anything about Emet-Selch being solely responsible, just that he made one for Azem despite their abdicating their seat in the wake of the Final Days made doing so taboo), but served different purposes between the Paragons and their sundered cohorts. To our knowledge none were used for that purpose during Amaurot's time, though Lahabrea sealing Hephaistos into one such crystal, Erichthonios making the one that instigated the Pandaemonium incident, and making one for Azem being taboo due to their abdication (which implies they were made for other Convocation seat holders at some point in the past) tells us the knowledge of how to make them was out there.

The Ancients' Final Days were slightly different than the one recently experienced on Etheirys. In the Ancients' time, the negative Dynamis forced their creation magicks to summon horrible monsters against their will as opposed to, well, whatever they wanted to make / summon (Emet-Selch specifically says that where prayers give rise to primals, the Final Days negative dynamis flood caused them to summon their deepest fears as Terminus Beasts / Blasphemies). Contemporary Etheirys' Final Days, due to the peoples' lower aetheric density, caused them to transform right out into Terminus Beasts / Blasphemies because they were more susceptible to dynamis-based attacks.

We know modern peoples' souls were also annihilated (or nearly so) upon transformation, but we don't know what happened to the Ancients killed by Terminus Beasts. Without anything stating to the contrary we have to assume that their souls were not annihilated and returned to the Lifestream. (The Terminus Beasts, specially powerful Blasphemies not withstanding, largely use the same model(s) as a cost saving measure. This is still an MMO, and reusing assets is far from atypical.) Besides which, as Meteion tells us in Ultima Thule, the souls of people turned into Blasphemies / Beasts (and those killed by them?) aren't annihilated per sé, just sent to her Nest so as to prevent them from being reborn. With her death (defeat?), presumably they will return to the cycle of souls.

The aether / dynamis relationship is more along the lines of matter / dark matter (or dark energy); I don't recall it ever being compared to antimatter.

... but yeah, don't think too hard about it. Magic, and they can always retcon or revise how it works to suit their story needs / interests.

[Lyth]

Dark Matter/Energy was probably the inspiration for Dynamis, but it's probably easier to think of it in terms of how the Fundamental Forces (gravity/electromagnetism/strong/weak forces) are influenced by differences of scale. Gravity is a relatively weak force, but it becomes a dominant effect governing movement when you look at larger distance scales with bigger masses. If you move to smaller distance scales with smaller masses, other forces start to dominate and the effect of gravity becomes negligible in comparison to the others. Aether is the dominant 'force' on Etheirys because there's a large quantity of Aether present, which in turn suppresses the effects of Dynamis. When you move further away from such places (like in Ultima Thule), Dynamis becomes the dominant 'force' governing natural phenomenon.

We historically associated life with Aether, given that our own souls are made out of it. Creation magic generally gives rise to arcane beings, but can't give them a soul. So there are a set of natural laws around Aether governing how it gives rise to life. Over on Ultima Thule, we have the Miw Miisv, which is a completely new species born entirely out of Dynamis, indicating that life doesn't need to be based off of Aether at all. They're two different systems of natural laws, each of which can produce real effects under different conditions. I think as we get more examples of Dynamis, we can start to piece together the underlying 'rules' of each system.

I don't think we have an adequate explanation around the Final Days of Amaurot. Each region had an 'index case' that was responsible for the sky changing. For example, the sky over Thavnair changed only after Khalzahl transformed into Svarbhanu. The problem is that the Amaurotines cannot directly be affected by Dynamis. So if we hold that to be absolutely true, then the index event can't be an Amaurotine themselves. It also means that Dynamis cannot compel them to summon a Creation against their will. What's more likely is that their Creations all individually turned, and then slew their masters. Places like Elpis and Anyder, with lots of Creations present, would be overrun nearly instantly. We also don't have an explanation for the 'terrible cry' as far as I know, but we'll leave that as a dangling plot thread for now.

I think the Convocation stones are intended to be analogous to 'job stones', in that they have memories of their previous owners stored on them. As for who you're summoning with the Azem stone, during the Thaleia storyline G'raha sends the player off to investigate the Heavens with their 'adventurer friends', indicating that you're canonically summoning other people you've met on your travels (through Party Finder).

[Turnintino]

For example, the sky over Thavnair changed only after Khalzahl transformed into Svarbhanu.

Because I just recently reviewed these scenes (was picking random ones to see how my character looked after some aesthetician changes lol), I wanna interject real quick to say that the script goes out of its way at one point to clarify that Blasphemies are appearing elsewhere without any changes to their respective skies... Which, ultimately, I'm sure was a contrivance to hand-wave the unaltered world states of other zones that EW role quests would later reveal were nonetheless affected. I don't think this means that the domino effect we seem to see play out in Thavnair is purely coincidental, because that's clearly not the story we're being told in that instance. But the contrivance, as it's presented to us, does still mean that the signs are/were not necessarily so linear, on either the modern Etheirys or the Ancients', as Emet previously described. And, as you said, there are big differences between the manifestation of our End of Days and theirs besides. Still.

Anyway, I completely agree otherwise. Love your comparison of aether/dynamis to the fundamental forces; so much more neatly explained than I usually see it (and struggle to do myself).

[Brightamethyst]

As part of that, the Echo doesn't 'tell' you about telegraphs and AoE fields.... as the devil is always, in the detail. We have ability telegraphs and AoE fields on screen for pretty much everything, even for things that have no souls/aether like boulders and machina which if it really was the Echo telling you that, it would only be able to work with something that has a soul. As inanimate objects/non living entities with no aether/souls also give ability telepgraphs/AoEs, therefore it's not the Echo showing that. It's just a gameplay mechanic with no bearing on the story. The whole game visual interface is just for gameplay purposes, nothing more.

Yeah. While personally I like the "red circles and cast bars are the Echo letting you see 5 seconds into the future" headcanon, it's just that. Headcanon. There's nothing in game that indicates it's an actual Echo power. It's much more likely that it's just one of the many mechanics that exist purely for gameplay reasons, lore need not apply (aetherytes in Elpis, Eorzean gil as a multiversal currency, etc.)

[Eisi]

it's just one of the many mechanics that exist purely for gameplay reasons, lore need not apply (aetherytes in Elpis, Eorzean gil as a multiversal currency, etc.)

1. Aetherytes in Elpis I 100% take as proof that they used Aetherytes in the Ancient world, along with the one in dream Amaurot. Why else would they get their own special model? Could have just as easily made something that's not an aetheryte.

2. Gil as multiversal currency I assume doesn't refer to the First where they went into detail on why Gil is the accepted currency there, which is actually an indicator that they take the lore more seriously than just having stuff exist purely for gameplay reasons (much like the new custom delivery line where spontaneously flying creatures [mounts] are researched). Instead you probably mean Ultima Thule, which only has been given shape through the sacrifice of Thancred, which made it breathable, traversible, tangible, communicable and I would assume also allowed for trade and stuff. Also we have the likely original Omicron currency as a counter as well: Omnicoin.

By the way, they obviously use it for gameplay reasons first and the lore follows that, rather than making the world reflect preexisting lore. It's still lore though.

[Brightamethyst]

2. Gil as multiversal currency I assume doesn't refer to the First where they went into detail on why Gil is the accepted currency there, which is actually an indicator that they take the lore more seriously than just having stuff exist purely for gameplay reasons (much like the new custom delivery line where spontaneously flying creatures [mounts] are researched). Instead you probably mean Ultima Thule, which only has been given shape through the sacrifice of Thancred, which made it breathable, traversible, tangible, communicable and I would assume also allowed for trade and stuff. Also we have the likely original Omicron currency as a counter as well: Omnicoin.

I was talking in a more general sense about the fact that any single currency is accepted absolutely everywhere. From Gradianan merchants, to Vanu Vanu warriors, to the Steppe clans, to 4000-year-old Allagan nodes in Azys La, to Ancients in time before time Elips, everyone accepts and pays out Eorzean gil.

In major trade cities like Kugane and Radz-at-Han (which we know have their own currencies)? Sure, there are probably money changers everywhere and those merchants probably accept loads of different currencies. But everyone else? When a Yanxian peasant gives you a quest to weed his fields, is he really paying you in gil, or is he paying you in local coin and the game just automatically converts it to gil for the sake of convenience?

[Eisi]

I was talking in a more general sense about the fact that any single currency is accepted absolutely everywhere. From Gradianan merchants, to Vanu Vanu warriors, to the Steppe clans, to 4000-year-old Allagan nodes in Azys La, to Ancients in time before time Elips, everyone accepts and pays out Eorzean gil.

In major trade cities like Kugane and Radz-at-Han (which we know have their own currencies)? Sure, there are probably money changers everywhere and those merchants probably accept loads of different currencies. But everyone else? When a Yanxian peasant gives you a quest to weed his fields, is he really paying you in gil, or is he paying you in local coin and the game just automatically converts it to gil for the sake of convenience?

What about language, does everybody in the world also speak the same language, except for some very rare cases? Do we have to assume that for the player's convenience the process of translation between different NPCs is shortened so it just appears that they understand each other?

I'd rather assume that unless stated otherwise, everybody speaks the same language. Same goes for Gil, it's a universal currency because it is. Just like there exists an unlikely explanation on the First as to why they use Gil, so does such an explanation exist for every other example you mention.

[Enkidoh]

What about language, does everybody in the world also speak the same language, except for some very rare cases? Do we have to assume that for the player's convenience the process of translation between different NPCs is shortened so it just appears that they understand each other?

I'd rather assume that unless stated otherwise, everybody speaks the same language.

It's been somewhat ignored for simplicity's sake here in ARR, but 1.0 explained this in better detail, that language is not universal on Hydaelyn, although the citystates of Eorzea all shared the same language, the beast tribes did not, and therefore other lands like Garlemald and the Far East would also have their own languages too (and it was actually mused by certain NPCs in 1.0 to be one of the reasons there was so much animosity between the citystates and the beastmen that was leading to Primal summonings, it was simple inability to effectively communicate between societies that was the cause of much tension, which, unspurprisingly, was being exploited behind the scenes by the Ascians). Even the moogles had their own unintelligible language - the fact that the player's character could understand easily what moogles were saying was the first indication something very strange was going on in 1.0's Gridanian storyline.

The Echo was therefore used as a convinient tool to both make use of this for dramatic tension and also neatly sidestep gameplay issues where it was easy to just have every NPC speak the same language from your perspective with a ready explanation as to why that was possible (and even that was not universal, as it was clear that not every Echo user actually had the ability of xenoglossy - there was a funny scene for instance in 1.0 where sylphs invaded the Waking Sands and not even Minfilia could understand what they were saying - she had to literally get the player's character to translate Sylphic for her).

Needless to say, ARR changed this somewhat where this whole thing was kind of brushed over with minimal explanation and everyone just speaks the same language (although the Ascians were initially depicted as speaking their own outright alien language, and this even popped up in ShB and EW from time to time with Ancients also speaking alien-like gibberish, and yet other times the Ancients could be easily understood, especially when the player goes to Elpis, so it still was rather confusing.).