User blog comment:Purehito/What is your favourite magic and what magic would you like to see in the next FT arc?/@comment-86.70.179.113-20130627075046/@comment-7418318-20130627111104

Considering it killed many Dragons, I wouldn't be surprised if Acnologia absorbed a multitude of elements from those Dragons and just like Natsu can make a lightning-flame Dragons roar, Acnologia probably can combine it's own roar with all those absorbed powers.

Since Etherion itself is also a combination of different kinds of magic, it's hardly surprising that such a multi-combo roar would look similar.

As for the one magic, if Lucy and Layla are right, it's highly unlikely that a being like Acnologia would achive it.

People at times say that the strongest predator of a certain area "rules" over it, like the Lion being considered the king of the savanna. I think F-Rogue meant something similar when he said Acnologia ruled the world, rather than being literal in the sense of the Dragon governing over the survivors. It might be the same for the title "King of Dragons".