User blog comment:Miskos3/Fairy Tail 531: Pegasus vs. Black Dragon/@comment-25324252-20170414232633/@comment-7418318-20170416073446

True, but then this is what Acnologia was from the very beginning.

He didn't finish off Gildarts and on Tenrou the protagonists even pointed out that Acnologia is just playing around with them, before he casually blasted them so hard that it could have wiped out the entire island.

For Acnologia that instant killing of Serena was out of character and how he's back to what he's been like before that... though I wish this "being how he used to be" would extend to him not talking to the "insects". I liked him more when he stayed silent instead of trotting out lines from the villain-101 handbook.