User blog comment:IamJakuhoRaikoben/Chapter 294: Battle of the Dragon Slayers, Review./@comment-3555799-20120804002715/@comment-4388213-20120804015756

Yeah apart from it being intially stronger a DS, the details of how it's learnt are sorta inconsistent. Hopefully Orga could shed some light on it later. But that to has a link to Zeref.

But my hunch is their's someone else pulling the strings in this play, Zeref doesn't seem all that evil to me it would seem he was tricked into it or just used.