User blog comment:IamJakuhoRaikoben/Chapter 470: The Hybrid Theory, Review./@comment-6401212-20160125204856/@comment-6401212-20160126055146

Zeref, possibly August and God Serena should be challenges at the very least. Acno's the Dragon King and the Dragon Slayers were made to try and defeat him for that purpose. One of the strongest characters to date, who is a Dragon Slayer with multiple elements, is just one-shot like that? I hope he isn't down, he didn't even get a chance to attack Acno yet. In an actual fight, I imagine Acno having some difficulty at least.