User blog comment:Miskos3/Fairy Tail Chapter 486: The Fourth Guest, Review/@comment-4507125-20160524082154/@comment-7418318-20160529063830

I think we can pretty savely discount Arkasios' theory on Acnologia being changed by Zeref by now.

Thanks to all the backstory we know that Zeref was still a good person by the time he sent the young Dragon Slayers through time and that whole time-travel plan was specifically executed to counter Acnologia.

What reason would a not-yet-bad Zeref have to temper with Acnologia? If Zeref was involved in the Dragon Civil War I think we'd have heard about it in his flashbacks.