I know we've argued this before, but here is another loose theory that Mythworld might be Earth.
I was playing a bit of TFL, and I noticed this Flavor Text:
"Not a palm's breadth free of wounds on his body, Five Motion Bloody Jaguar knelt to kiss the earth and drawing strength from her rose to charge the thickest gathering of the enemy."
-Journeyman Flavor Text, Myth TFL
Now, it says that he "knelt to kiss the earth." While this is hardly conclusive evidence (Especially because of the fact that earth is not capitalized and that any dirt can be described as 'earth'), please notice the next part of that sentence. "and drawing strength from her." Her?! If I was kissing simple earth, I would say 'it.' But if I was kissing [Mother] Earth, I would most likely say 'her.' Unless this journeyman had a girlfriend named 'earth,' in which he didn't respect her enough to capitalize her name, I would add this to the Earth theory.
Feel free to dispute this as I know half of you will.
Zandervix