User blog comment:IamJakuhoRaikoben/Chapter 449: Mavis & Zeref, Review./@comment-203.215.121.60-20150825123224

Zeref said that Mavis had the potential to walk alongside him. That's because both him and her are geniuses. Zeref probably thought that Mavis is the same as him which mastered Black Arts, but I think that Mavis curse is not dark or bad. It's Light which is the opposite of Zeref's. And I know people below are thinking the same.