The Spirit World is the beating supernatural heart of the ATLA and LOK universe, a lush, radiant, and ethereal plane of reality full of ancient lore and mystical secrets. It runs mostly parallel to the mortal realm, otherwise known as the physical world, yet the two have also been known to intersect in fascinating and dramatic ways. For most of history, the denizens of each world have lived mostly apart from the other, with only the most spiritually gifted mortals able to cross to the Spirit World at all.
(ATLA, 1.20, 2:45; 7:37)
But fear not, intrepid reader. With this humble bestiary crafted in the style of the Ancient Chinese Shanhaijing, you too can explore the mythic landscape that is so integral to the shows (and our study of the monstrous within them)! The creatures and phenomena that you are about to witness up close will inspire wonder, awe, curiosity, fear, or a potent mix of all four, but be careful not to show them anything but proper respect. They are more powerful than you can imagine, and they exist outside of the bounds of your own value judgments, as part of a timeless, complex, multidimensional ecosystem that is your privilege to be able to encounter.