I'm starting to think Acnologia is an Ethernano Dragon.
- His Dragon's Roar is the same colour as the Etherion ray and, like Etherion, it can destroy an entire island or city.
- His appearance is similar to that of an Etherious, who are also made from Ethernano.
- According to Arcadios, Zeref turned Acnologia into a dragon. His theory is probably because of Acnologia's appearance and the fact that Zeref's demons, as stated before, are made from Ethernano.
My theory is that as a human, Acnologia was a Ethernano Dragon Slayer. Dragon Slayers can enter Dragon Force by eating Ethernano and if Acnologia was an Ethernano Dragon Slayer, then he would've had a habit of entering Dragon Force a lot when fighting. So either his Dragonification was due to over use of Dragon Force, meaning his Dragon form is now his Dragon Force or Zeref cursed him. Either way, the reason for his appearance could be due to wielding Ethernano.
What do you guys think?