Originally Posted by Fat Mario With Lasers
This seems extremely plausible (except for that last bit, it's most likely a gym). This also helps associate typing with them (assuming that the typing will reflect the mythology).
Xerneus is probably going to be either part Grass, Ground, or Rock, most likely Grass imo due to the whole tree-thing (and being inside a forest and everything), not to mention Grass is pretty much the Nature-type, which is more fitting than Ground or Rock. (Grass / Electric :DDD)
Yveltal is definitely part Flying, as most people have speculated, but I think this makes the other theory (Dark/Dragon or Fire with Levitate) much less plausible than Flying / Dark (or even Flying / Ghost, I'm calling it right now, Flying / Ghost)
Z-Mon (rip Zygoat :'[) will most likely be part Dragon (not sure about Water, it would fit the Land / Sky / Ocean theory, and iirc it was interpreted as a Sea Serpent, but I know little to nothing about Norse Mythology), although this one is pretty much impossible to say, since we don't actually have artwork of it (It could also not exist, but this is unlikely - GF loves to make Legendary Trio's). It also helps that a serpent-like creature is probably the easiest to make a Z-shape with (Although I secretly wish for a goat with a Z-shaped head piece because Zygoat is the best name ever :])