Chi-Lin isn't in the real world, but in Another Dimension where the beliefs held by people in the real world (even those long dead) have made every mythic figure real.
Or it's just a universe not related to ours where the creatures do not have to follow the same mythology as in our world, just borrowing look, name and possibly skills. In fact, say, a Medusa could be a fairly common monster in the wilderness.
Inverted: Dozens of cultures exist at varying levels of technology, but all share pretty much every other aspect of their way of life.
Subverted: After meeting with beings from various mythologies, Chi-Lin discovers there was really only one true cosmology, and a race of shapeshifters has been pretending to be creatures from other mythologies to spice things up.
Except, those shapeshifters liked it to so much they became the mask quite literally.
Alternatively: They're shapeshifters from a different cosmology.
Alternatively: ...Except for the vampires. The shape-shifters have no clue where those guys came from.
Naiads fight Puca for control of river-turf, werewolf-centaurs become a public hazard, Chinese and Western vampires routinely have your-sire-is-so-fat joke bouts, werewolves are often sued for chasing nekomatas up trees, Quetzalcoatl, Zeus and Thor spend every Saturday seeing who can prang the most mortals with lightning bolts, and Satan and Cthulhu can often be found having staring contests.
Kids trap a Spaghetti Monster and a Shoggoth in the same bottle, then shake it to see who wins the fight.
Zig Zagged: Everything is real! Except it was just a guy in a mask. But he was part of a double-masquerade, designed to distract from there actually being plenty of weird stuff. But then it turns out that Chi-Lin was having a fever dream. Only then she learns she was in a Lotus-Eater Machine, then learning that she was in an experiment being conducted by Aliens from the 30th century. Said aliens turn out to be props in a 30th century amusement park.
Averted: Chi-Lin encounters only those fantastic beasts and other figures which belong to her cultural setting.
Enforced: "We're going to run out of mythical creatures eventually, plus we don't want to seem culturally insensitive. I know! Lets make every mythology true!"
Discussed: "So, every myth is true? Wow, I guess I really should give our ancestors credit for being on the ball with all those legends they passed down."
Conversed: "So, if all of these cosmologies are real, how come all the leprechauns stayed in Ireland and the Kraken only attacked Greece?" "Eh. They may be magical, but I'm guessing they live in ecosystems and don't like to wander. Still, it'd be awesome if Satyr's opened a Hydra-Head-Burger in Dublin."
Deconstructed: Chi-Lin has a crisis of faith. If everything is real, can anything be true? She questions all the varied creatures and deities, but even they have no clue on the true workings of the cosmos.
In the end, faced with the fact that faith may well be creating an incredibly diverse spirit world, she resolves that though Atheism is probably the easiest choice, she'll instead turn her and others' faith into creating a new cosmology of mankind's conscious choosing.
Alternately, a world where anything and everything is possible is just that...a world of infinite possibility, and therefore one demanding infinite optimism.