User blog comment:Inept Wiki User/Speculation: Acnologia and Assimilation/@comment-4488668-20130522174815

He's called "The Black Dragon", so he originally probably had "Black Dragon Slayer Magic", or something like that, which eventually merged with the elements of the dragons he slayed, and became a mixture of elements similar to Etherion. I love your theory! It makes so much sense regarding Acnologia's element.