User blog comment:FairyRaven/Fairy Tail Chapter 399: Wings of Despair, Review and Commentary/@comment-5894890-20140908165543/@comment-24066070-20140908171401

Acnologia's appearance makes sense to me.

If a few bursts of Zeref's magic was enough to lure it to Tenrou, then all the Curses used by Tartarus should certainly be enough.

After all, Tartarus' members were created by Zeref, thus they must bear his "signature" is some way. It is also likely that Plutogrim and Alegria were developped by Zeref and these things kinda stand out.

Not to mention Zeref himself decided to drop by, pulverize a sword and warp away again.