User blog comment:IamJakuhoRaikoben/Chapter 449: Mavis & Zeref, Review./@comment-24277053-20150825021552/@comment-112.208.228.110-20150825042414

A filler arc can be put in between Avatar and Alvarez arc. They can probably go on a mission before Mest arrives and tell them about Alvarez. Then Fairy Tail Zero can be inserted when Mavis tells them her story. (Between chapters 448 and 449)