Something I find interesting related to the Sub Zero Emperor / Galuna Island arc is that they tell us that demons can't even get close to the Moon Temple. But that's not completely true...
Because Etherious can get close to the Temple and they are also classified as demons. So it must be only normal demons that can't get near it. After all Natsu was clearly able to get into the Temple. I would also argue that it can't just be chalked up to whether or not Mashima decided to have Natsu actually be a demon when the arc was created, because Deliora was arguably closer to the temple than any of the demon villagers ever got. Deliora is also an Etherious literally known as the "Demon of Destruction."
Makes me wonder about demon classifications. Like I guess Mirajane and Minerva might still be able to get into the Temple despite having more demonic essence than the average human. Since their demonic essence is more compared to or related to Etherious than the Galuna demons.
Anyway I just thought it was interesting that natural demons have "too much darkness" and therefore can't go to holy lands but artificial demons like Etherious are some how fine?