So here's the thing. I like D&D. I like fantasy. My friends like both these things, and Smite. I think I like culture, and seeing the way it intersects and weaves its way from place to place through time.
So naturally, I want to start investing time into reading other mythologies and semi-historical documents, both out of personal interest, and to help my own interest in writing and media. All stories can be traced back to these older ones, so it makes sense to have a good grasp, especially if I plan on incorporating aesthetics and ideas into my own works, especially if they're from non-european cultures, so that I could portray these ideas accurately (for example, I lived in Japan for five years, where I met my friends, and we're thinking of doing an Asian-themed D&D game).
I've already read Edith Hamilton's "Mythology" (when I was in Middle School), Beowulf (Heaney translation), 90% of the Bible (not very relevant, I know), and Crossley-Holland's' "The Norse Myths" (all while I was in high school). Oh, and I was homeschooled, which means I'm probably lacking a bunch of necessary historical context. I'd like to try and focus primarily on the stories themselves, without too much outside or opinionated commentary unless it lends historical context of the era or people who later added to the text. I got two pages into Donald A. Mackenzie's "Myths of China and Japan" only to realize that it wasn't a retelling or a compilation of canon, but rather an analysis about proving that China had borrowed it's myths from other cultures and had never had an original thought.
Which finally brings us to my main point. To be honest, I'm kind of feeling a little overwhelmed by the sheer volume of historical and mythological works I'm going to have to read. I assume this is partially because most mythologies aren't as well organized or documented as Greek myths are.
Like, is it better to read a retelling of the story, like Edith Hamilton's Mythology and Crossley-Holland's the Norse Myths? Or should I read the original documents like the Edda and the Odyssey? Where do works like Journey to the West, the Vulgate, and Le Morte d'Arthur fall (because they seem to occupy this weird middle ground)?
How grounded in real history should the versions I read be? What if there aren't any good sources at all and all we have are vague scribbles accompanied researchers notes? How important is historical context? How much should I know about the culture beforehand? Where would you draw the line between coherent stories, and random bits and pieces of folklore? Should I go from oldest to newest, for accuracy's sake, or should I go from newest to oldest, because those will be more readable and entertaining? Do the majority of these documents and works veer more towards dry and boring, or surprisingly straightforward and entertaining (like Beowulf)?
TLDR; I am archive-panicking over the sheer volume of sources and works regarding mythology/ancient fantasy/ancient religions, and I could really use a starting point. Particular interests include Japanese, Chinese, Arthurian, and Mesoamerican works. Considering reading Dante's Inferno as well.
I'm going to answer this in two parts, though it goes outside the field of history.
Part one, what is myth?
This might seem like a stupid question, but I think modern people have a difficult time fully acclimating to the societal context of what we now call mythology. To get the mindset right, I'm going to point to a piece of modern myth; The Boston Tea Party. Before anyone goes biting my head off, I'm not saying the Boston Tea Party didn't happen. I am saying that the Boston Tea Party is a formative myth. It is a centralizing part of the story of 'America', how 'America' came to exist, and what 'America' is about. It is a modern myth, a formative story important to the image and foundation of the American nation.
That's what myth is.
Myth is formative, centralizing, even historical stories of how a people came to be, what their culture values, and explanations for why the world is the way it is. It's not just stories, or names of gods people worshiped (though this things are part of myth). Myth is the act of structuring the world. We today of course recognize that the moon is a celestial body distinct from the Sun, but central American myths explained the moon as a dimmer sun, created by the gods from the body of another god who wasn't brave enough to sacrifice himself and become the sun until some other god did it. So the other gods made the moon dimmer.
And not all myths are necessarily about gods or supernatural beings. Minamoto Yoshitsune, Achilles, and Ce Acatl Topiltzin Quetzacoatl are all in different ways fusions of past events and supernatural elements. The stories people told about them were mythical. These men and their lives became formative stories. And myth gets messy that way because it mixes the supernatural, the religious, the real, and unreal into a whole.
In this regard, historical context is very important. Mythology does not simply spring from nothing. When someone writes a book about Chinese mythology and says they got a lot of their ideas from other places that is important information because where those ideas come from and how the Chinese incorporated them into Chinese Myth tells you a lot about the history of China. It tells you who they were in contact with. What relationships they valued. What societal structures mattered to them.
Backtracking myths is a laborious process for academics but an important one as well, because myth is not static. They change. Why do the Greeks have more than one sun god? Because what we call the 'Greeks' evolved their mythology as their culture zone expanded, as they absorbed new groups into their culture, and thus new ideas. All cultures do this. Sometimes new myths replace old myths. Sometimes they mix. Sometimes they come to exist side by side.
And this is broadly something a lot of fantasy doesn't do very well (though notably, Tolkein knew this very well from his academic background and incorporated it into Lord of the Rings). So, I would say that you definitely want historical context. You want to understand what myths were valued at what times and in what ways. Myths are not just pantheons of gods and stories people told. They were central to how people understood the world and their place in it, and very often conveyed moral content.
To what I can actually recommend:
If you want to delve into Mesoamerican mythology, I'd first recommend grounding yourself and I think the best resource you'll find is over on Audible; the Great Courses lecture series Maya to Aztec: Ancient Mesoamerica Revealed. I love this lecture series. Barnhart is a great lecturer and the series will go through the list of what we know, how we know it, and note what we don't know. He also covers Mesoamerican mythologies and how these myths centralized social life, right down to how the peoples of Mesoamerica built their cities.
Once you've done that, there's a lot of resources you can use.
The Flayed God: The Mesoamerican Mythological Tradition is great. Barnhart's lecture series will prep you for it too. The book covers a number of prominent and recurring themes in Mesoamerican myth, including several Barnhart mentions and then kind of skims over because his lecture series is trying to cover a lot of ground. I think these two resources go amazing together.
You can find a lot of the primary sources behind these works too. The Florentine Codex, the Codex Borgia, the Dresden Codex, the Codex Nuattall, and others. They've all got reproductions and printings out there, some with commentary, some without. I'd recommend physical copies. I have some ebook versions and (glaring at the Dover version of the Codex Borgia in particular) they're not the most readible in ebook format. A physical book with the ability to flip back and forth on the fly is going to be your friend.
From there, you can always delve deeper. Mesoamerican history, archeology, and anthropology are fast moving these days. We're finding new stuff constantly and JSTOR would be especially friendly for you on this topic if a local university or library has a subscription.