Consider how many times people have messed with Harry's head or tried to reduce it to mush.
That seems insufficient to explain the severity of his headaches, when he heals so quickly and completely that broken bone scars disappear in a couple of years. I think instead that the prominence of Harry's headaches in the books, is Jim's way of telling us there is something going on in Harry's head, and I think it's repressed memories like the memory he recalls of the fight with He who walks behind in Ghost Story.
No, it was Morgan le fay's Athame.
The only le fay I remember from the books is Margaret le fay Harry's mother. Where is Morgan le fay mentioned?
WoJ and possibly her acting as the Parasite.
So Jim has stated categorically that it was Lash? That seems unlikely, Bob said she was gone, that the soul Harry had given her was no longer in Harry's head didn't he?
Harry and Ebenezar for starters, we've also apparently been introduced to 6 of the people who showed up at Chichen Itza with grey hoods (excluding Harry, Ebenezar and Vadderung).
I believe I remember Harry stating that 13 (a coven) showed up, so that leaves 5 we don't know, but of the other 6 that we do know, who are they? Injun Joe was supposed to be sick. Martha Liberty? The Gate Keeper? The young wardens had been captured along with Captain Lucio, only Chandler was still free and in hidding, and none of them would I consider a Heavy Hitter anyway. The presence of Vadderung indicates that not all of them are necessarily from the White Council, but I can't think of anyone else we've been introduced to that can fling heavy magic around as they were, except for faeries and with Winter already there would Summer have shown up. So some of the older stronger wardens that apparently hate Harry? Hans the Toymaker was considered strong enough for the Senior Council maybe him? I'm stumped to think of who is on the Grey Council.