Exotic Imports

Question: How do you explain the origins of gods who are obviously imports from somewhere else? Co-locations of that god? Uplifted humans filling a fateful divine role? New gods filling a fateful divine role?

Each situation of a borrowed god - syncretized, visiting, or anything else - is different, so we always examine them on a case-by-case basis as they come up. There's no way to really make a blanket rule that would cover everybody, and depending on the mythology surrounding a particular deity, any of the options you mention and several others might be appropriate. (Well, okay, except for the human one, because humans can't become gods in Scion. Could be a Scion moving on up, though.)

Some gods are clearly borrowed by one culture from a neighbor, retaining most of the same features and personality; a good example is the borrowing of Aphrodite to become Rome's Venus, who is almost identical to her in every way and has only minor changes here and there that occurred as the new culture added its personal quirks to her legends. In these cases, it's usually best to rule that this is in fact a case of the same goddess being worshiped by two different cultures, something that happened all the time in the ancient world and is certainly not hard for a goddess to pull off if she puts her mind to it. As a Storyteller, you're free to have her show up in whichever form she feels like it and on whatever turf she pleases, because she's just a multicultural deity rather than a true split personality.

On the other hand, some borrowed gods have been syncretized with a local god to form a new synthesis, one that clearly shows both roots but no longer properly belongs to either. A good example is Shango, who in the New World was syncretized with Christianity until he formed the bizarre combo-pack of St. Barbara of Cuba; because incoming Yoruba slaves were not allowed to worship their gods openly, they used Christian placeholders instead, and Shango was assigned to St. Barbara because she was traditionally shown wearing red, one of his symbolic colors, was associated with lightning thanks to the story in which her murderer was killed by it, and was the patron saint who guarded those who worked with firearms and explosives, which matched the temperamental African god's personality. The result, centuries later in Cuba, is a potent religious figure in Santeria who is no longer really either one, carrying equal qualities of the Catholic saint and the Yoruba god, but not really matching up to either anymore. When something like this happens, there's more leeway as a Storyteller to try to figure out what might have happened; you could again say that it's simply one of those two gods using the other as a persona or disguise while in a different land, but you might also decide that Shango becomes Barbara when he goes to Cuba thanks to the weight of Fatebonds forcing him to, or that the new god, so suspiciously similar to Shango, is in fact an ascended Scion of his who took on one of his roles at godhood. There's no single best answer except what you think will be the most interesting for your story.

And finally, there are the gods who are definitely imports but also definitely fully separate and distinct Legend 12 gods in their own right; the example we usually use is Avalokitesvara, a many-armed Indian god on a mission to aid humanity, who in China becomes Guanyin, one of the most popular and widespread goddesses with a plethora of Chinese-centric origin stories and myths. Avalokitesvara is certainly an important dude, but at the same time it would be ludicrous to claim that Guanyin, who is a Legend 12 goddess if there ever was one, is merely an offshoot or disguise he sometimes wears. When you've got this going on, you can decide to treat one as an aspect of the other, but that leads to weird chicken-and-egg questions - we'd normally say that Avalokitesvara is the occasional aspect of Guanyin when she goes to India, since she's more important and probably higher-Legend than he is, but at the same time we know that Avalokitesvara was worshiped significantly before she was, so what gives there? You could rule that she decided to leave India and become Guanyin, but then you're making a weird call that gods who have counterparts in other religions may not exist at all, which is a big bummer for the gameworld. Instead of messing with all of that, we generally rule that if two gods have different personalities and are important in different religions, they're two different people, regardless of whether or not we know sociologically that they came from the same source. After all, we're not about to decide that every European sky god is really just a face of Dyaus Pita, so there always has to be a line drawn somewhere about what you decide to syncretize and what you let be itself. That might mean that these are two related gods, a god and another god who copycatted him in order to get a free ride to fame, a god and his Scion that took over the mantle in a new geographical area, a god and a lesser immortal or even Titanspawn aspiring to godhood, or anything else.

At the end of the day, our inclination is usually toward syncretizing as little as possible; if it's not obvious that they're the exact same person and have nothing to offer separately, we prefer to keep different gods across the pantheons, letting them represent their cultures and religions in their own way. But it's always a decision the Storyteller has to make to best fit their plot and gameworld, so it'll never be exactly the same across the board. And it really doesn't need to be, so no one should feel stressed about doing it wrong.