And in the series finale it was revealed that Agatha possessed a significant spellbook that's had a few appearance in the Marvel universe – The Darkhold, AKA the "book of the damned", which she uses for various spells in the series before Wanda takes it for herself later on. (Read our WandaVision review for a full recap of the finale, but beware of spoilers.)
So, what is the Darkhold, and what could its significance be to the future of the Marvel universe? We have a some answers.
What is the Darkhold?
In the original Marvel comics the Darkhold, also known as the Book of Sins, is a grimoire (or magical textbook) that crops up a few times in various stories, first emerging in the 1970s and continuing to appear from time to time over the decades.
The Darkhold was written by a demonic Elder God called Chthon, and was so full of magic and power that it was impossible to destroy. Among its uses in Marvel’s fictional history were creating the first vampires and werewolves by use of spells, and it passed through the hands of various heroes and villains (including Doctor Doom, Morgan le Fay and the High Evolutionary) over the course of its appearances.
More like this
And as for the Darkhold’s connection with Wanda? Well, in the comics Wanda grows up as an unwitting vessel for Chthon, who was planning his return after a previous banishment. Possessing her and defeating the Avengers in her body, Chthon used the Darkhold to begin a ritual to bring himself back to Earth, but was eventually defeated when Beast stole the book and helped Wanda imprison Chthon in a doll.
In a later story, Chthon returns to face off with Wanda again, though this time he possesses her brother Pietro and uses his super-speed to rush around the world reading the powerful words of the Darkhold to anyone he can, before being defeated and imprisoned within the Darkhold itself.
Later still during another storyline Chthon possessed Wanda once more, before being removed from her body by Doctor Strange.
Has the Darkhold appeared in the MCU before?
Though the WandaVision version has a new look, this isn't The Darkhold's first Marvel Cinematic Universe appearance. As many fans have noted, the Darkhold was an important artefact during several episodes of Marvel’s Agents of SHIELD, used by various characters to perform powerful magical acts (including interdimensional travel and attempting immortality) before the book was eventually hidden in another dimension by Ghost Rider Robbie Reyes (Gabriel Luna).
And that wasn’t the end of its TV appearances. In the third season of Marvel TV series Runaways the same book is used by supervillain Morgan le Fay, then stolen by the Runaways who use it to bring back heroes Cloak and Dagger and eventually send Morgan le Fay to the Dark Dimension.
However, it’s a little unclear how canonical we’re supposed to think either of these series. While Agents of SHIELD definitely started out as an intentional spin-off from the MCU and referenced the events of the films its own characters and story points (including the mutant-like Inhumans) were largely ignored by the MCU films themselves. Similarly, while Runaways was apparently set in the MCU it didn’t really reference the films.
In other words, it’s tricky to say whether these previous appearances of the Darkhold “count” – because if they do, there might need to be an explanation for why the book looks so different this time around.
Is the Darkhold in WandaVision?
Yes! In the final episode it's revealed that the book glimpsed in previous episodes is indeed the Darkhold, which Agatha mentions when telling Wanda about her status as the "Scarlet Witch" or legend, a being who can cast magic without the use of spells.
"There’s an entire chapter devoted to you in the Darkhold," she says. "That's the book of the damned."
Later, in a post-credits scene we see Wanda using the Darkhold herself (above), possibly in an attempt to understand her Chaos Magic or (based on the voices heard during the scene) trying to find some way to bring her sons Tommy and Billy back to life outside the Westview anomaly.
Is The Darkhold in Doctor Strange 2?
Given that we know Elizabeth Olsen is reprising her role as Wanda in Doctor Strange 2, Doctor Strange in the Multiverse of Madness, it seems likely that in some way Wanda's new focus on magic and the Darkhold will draw the attention of Benedict Cumberbatch's Sorcerer Supreme.
Perhaps he'll come to stop Wanda using the dark magic of her new grimoire, or maybe some spell she casts will need to be undone. Perhaps she'll even succeed in bringing her sons back, leaving Strange with the difficult take of removing them from existence once again if they threaten the fabric of reality.
Who knows? Maybe Wanda's the ultimate villain of the Doctor Strange sequel, fracturing the multiverse as she attempts to bring her sons back to life.
Or, alternatively, maybe Wanda just goes to him for help with her new magical outlook. Everyone needs a teacher, after all, and when it comes to magic, there are limited options in the MCU.
Still, whatever Wanda ends up doing, it seems like the Darkhold will be important to the story. We're betting this isn't the last we've seen of this particular perilous page-turner.
Want more WandaVision content? Check out our guide to the WandaVision cast, the WandaVision release schedule, Agatha Harkness and the creepy WandaVision commercials. Plus, we ask: When is WandaVision set and how did Vision survive?
WandaVision releases new episodes on Disney Plus on Fridays. You can sign up to Disney+ now for £79.90 for a year or £7.99 a month. Want something else to watch? Check out our full TV Guide.