I'm legitimately interested to see what's up with Zeref.
He didn't seem particularly LOL I DESTROY WORLD prone last time we saw him.
Right now I'm waffling between the last Zeref we saw being some kind of time travel/clone (meaning there are 2 of them kicking around), or Zeref is playing host to a Demon Lord, but neither the Demon nor Zeref can totally shut the other out, so they're trapped cycling control of the body back and forth between them.
Which would explain why Zeref wanted Natsu to kill him - that was HumanZeref hoping he could end BOTH of them.
Which, come to think of it, might be why they're trying to trigger Face - the demons have already stated that they will be unaffected, so presumably, if magic is destroyed, HumanZeref would lose the power to fight DemonZeref anymore, leaving Demon in total control.