User blog comment:TheCarrotSaysYumYum/FT0 4 - Dances with Blades, Review./@comment-24102956-20141023024834/@comment-4449950-20141023040311

I think you also forget that FT0 is set almost 100 years before current FT events. As such, something could have changed in Zeref over these 100 years that causes him to be out of control. I don't remember it being stated that he's always been having issues with his Death Magic (if so please correct me) so perhaps something goes wrong at this current time that causes him to lose it.