I wonder if monsters absorb the inherent magical energy of the dragon, and that's why it's so big?
Also yeah, having multiple biomes within a singular organism? Kinda reminds me of the Lion Turtles from Avatar the Last Airbender, but obviously on a much bigger scale. Or the main setting in Xenoblade 1, where they just have multiple full-scale civilizations and climates there living there.
I wish we had some sort of scale to refer for this thing. I mean, it blanketed an entire town with it's body but I kinda wanna see a normal human being next to it just to get a reference for scale. Because there's only so much "magic" can explain away. Though slowly learning more about the dragon's physiology and biology is interesting in it's own right.