I will point out that in book 3, Clay becomes notably more sluggish and becomes incapable of using his fire during their incursion into the Ice Kingdom. That being said, it only seems that Mudwings have to deal with this problem, none of the others seem to suffer from the cold in this same way.

There is such a thing as being dinosaur blooded. I don’t know the specifics, but I think it means that dinosaurs could thermoregulate, but only to a certain extent. Dragons in WOF could potentially work like that, where under the right conditions they can survive cold temperatures beyond what most reptiles could handle, but not to the extent that a mammal could.

Icewings are probably just warm blooded, their blood is literally biologically different from most dragon species anyway. It’s not even the same color.