User blog comment:FairyRaven/Fairy Tail Chapter 408: The Definitive Demon, Review and Commentary/@comment-24277053-20141110135803/@comment-1359322-20141111002754

Gray obtained some sort of foresight from a higher power and becomes Gray the Demon Professor. He now knows everything about Tartarus, from the exact numbers of Lamies to the secret relationships of Kyouka and Sayla.

Jokes aside, once again Mashima showed some inconsistency, when Gray first fought Tempesta, he had some shiny eyes thing that allowed him to know Tempesta was the one who poisoned Laxus and Raijinshuu, why didn't Gray use the shiny eyes this time. ( ._.)