As TCF shared
here, the next book might not be Mirror Mirror, but instead a book spanning the year between BG and the wedding, where Harry deals with his trauma and completes some sort of therapy.
Thinking about what a villain for such a book might be, I realized that BG kind of set up a scenario where Harry might create his own enemy.
- Per Bob, tulpas might have been generated in BG through collective fear and chaotic power. Tulpas are beings created from strong emotions, feelings, and thoughts. In Supernatural, a shared belief in something created that thing in the form of a tulpa.
- Harry is suffering from conjuritis, where his thoughts are manifested using ectoplasm.
- Harry's had a ton of mental trauma, to the point that he's going to have a book dedicated to it.
- Harry's more powerful than most wizards his age, and conjuritis is rare at his age, possibly to the point to the effects might not well be known.
So, let's speculate that Harry is going to have a nervous breakdown, and his conjuritis is going to create a tulpa from his power and fear.
What tulpa would you want to see created, and what would it do?Personally, I'd want it to be his Id self. Rather than being something attacking him, I'd want it to watch his deepest fears, literally. I'd want it to be a version of him that gives in to its desires and tries to kill things that Harry wouldn't (Mab, Marcone, Rudolph, ghouls, etc) in order to make Harry safer.
It'd need to not be evil, per se, because that would be saved for the mirror mirror version. And I think if they were similar enough but different enough, it could be done well, to the point that Harry having faced his own fears and issues in this next book would help him deal with the mirror situation better.