So as I've earlier eluded to, for the purposes of my retelling, Aideen and Garnok are the same thing. I have commited several flavour changes to the setting to accommodate this, just a heads up for that cause I couldn't possibly explain all that without some context first ^^"
For the remainder of this post I will be refering to Aideen/Garnok as "A/G" (as I've not yet coined a new name), using the pronoun it/its. Its specific titles will be used in case I touch on the individual beliefs of it's different followers.
So what does it mean they're the same?
For most characters nothing changes as they would have no way of learning this information early in the story - meaning most changes would occur in the part that has to be completely made up anyways ^^" But concerning the world-building aspects... there's a lot to go through.
Here's a (not so) quick over-view:
Jorvik's God
A/G exists outside of Jorvik, possibly in Pandoria... it's kind of unclear since it could just be severely tainted by its presence. I am like half-way on deciding whether Pandoric disease actually also originates from the A/G, because I don't know how to juggle multiple types of corruption... safe to say it's a work in progress. What is set in stone for me however is that Pandorians have formed some kind of symbiosis with the A/G.
I've thought of A/G as a kind of a cognitohazard - in Linda's words: "Knowledge is power," but the more you know, the more you expose yourself to its influence. What harm does that do, you ask? Madness mostly, the rest kind of depends if I am merging it with the Pandorian thing or nah - then we could really take it off the rails B)
Everyone sees A/G differently, according to what they believe or imagine it to be. The legend of Aideen has left people under the impression it's a girl on a horse, the wildwood herds believe in a horse divinity and the people looking for Garnok in the depths of the ocean imagine it as sea monster - and it is what it is thought as. It may have a "true" form, but explaining something unknowable kinda... defeats the purpose ^^" Likewise, it's hard to tell whether A/G is sentient. Everyone assumes it is, but much like it's appearance, it appeals to the senses of its observers - a Chinese room of sorts.
Keepers of Aideen
Fripp has established the Keepers some time after arriving on Earth. It's likely he used it to spread the teachings about Aideen. Being corrupted by A/G, the best he could do to not let its influence spread further was to coat it's presence in legends that obscure the true nature of the entity.
The magic of the four circles has been passed down for long enough to be rendered harmless. There are hard limits however, as the cost of understanding these powers is obviously getting closer to A/G, rendering both the user and their abilities more unstable. Those who train young keepers tend to pass down the theory rather than skills and make sure to steer their apprentices along the threaded path - control is instrumental.
Dark Core
While it has changed names over the decades, it's a much more recent player on this field. Mr. Sands has probably come in contact with A/G by accident and his psyche was greatly damaged in the process, as if his recent loss wasn't enough of a burden. Despite that, Sands was able to persevere, working hard to fill the holes in his understanding of his "savior," either out of spite or because deep down he remained hopeful - in the end A/G only ever echoes his own thoughts.
Darko's slightly different. With him, Sands' endeavours finally started to bear fruit, and all it really took was throwing away the moral compass and stepping over dead bodies. Darko probably coined the name Garnok himself, and devoted a lot of resources into siphoning its power. One has to consider that Icarus probably felt warmth as he drew closer to the sun.
The (Dark) Riders + The Guardians
So they are the same kind of entity. I have cycled through a few versions until I landed on... well the easiest option by far - the fragments of A/G. I am inclined to say they're its children, but it's not entirely accurate. The reincarnation of Aideen (the MC + their horse) would also fall into this category, but for my intents and purposes, they don't wield all of G/A's power. It's probably just a little different flavour than what the other guys get - so just a 5th rider.
Anyways, they're beings that reincarnate over the ages. They adhere to a certain "formula" in regards to their appearance, but no reincarnation is ever the same and they never have the full picture of past events. Memory of their past life and their new self tends to clash, blending seamlessly into the ordinary world and yet being somewhat aware that they were never truly part of it. They're acutely aware of the A/G's existence and can always feel it's presence, with one key difference from everyone else - it's a blank slate to them, in fact, they mostly get influenced by other's perception of it.
The Guardians often find themselves by the Keepers. Fripp knows of their importance and has somewhat managed to take their reigns. As he hasn't been so lucky with their Riders, he had to improvise.
So yeah, that's the gist of it...
I am aware there are more things I have to answer for, like the Sentinel Trees, the Wild Weave, the Soulbond and so on... but this on it's own is getting a little too long ^^" We can get to it some other time! Or if you're curious about anything, you can send me an ask - just sorry if i don't reply immediately, I might need to do some deep thinking first :D
For the finish, here's a my version of Fripp, unprompted. I honestly wanted to draw more characters to illustrate my ideas better, but the show is on a budget (the budget is time and as we all know, there is no time in Pandoria)












