There's nothing Marvel loves more than a good key prop. After all, the entirety of the decade-long "Infinity Saga" was really just the fight over a handful of stones, and WandaVision appears to be no different. In Episode 7, Wanda's investigation into friendly neighbor Agnes' basement led to a shocking discovery about her identity, but it also included a peek at a mystical book with a long history in Marvel's televisual past. Warning! Spoilers for WandaVision Episode 7 ahead!
While on the search for her twins (who may or may not have been transformed into animals) Wanda discovers her neighbor's basement appears to be the one thing in Westview she can't control. The walls are covered in vines and there is all sorts of antique furniture. Displayed on a little stand is a mysterious book that gives off a menacing aura.
Before Wanda can investigate it properly, Agnes finds her and reveals her true identity. She's not "Agnes," she's Agatha Harkness, and she's actually a witch who's been behind many of the events at Westview.
What is the Darkhold in Marvel?
The Darkhold is an extremely prolific item, having appeared in over 100 comic books. Also known as the Book of Sins, the Darkhold holds an indescribable amount of eldritch-esque dark energy that could blackout a city — or possibly create one entirely.
In television, The Darkhold appeared in multiple episodes of Agents of S.H.I.E.L.D and Marvel's oft-forgotten series Runaways. Ghost Rider took the book to the Hell Dimension in Agents of S.H.I.E.L.D, but that wasn't enough to get rid of it apparently as the book showed up in the hands of the evil Morgan le Fay in Runaways.
The contents of the book were actually used to create a banishment spell for Morgan le Fay, but even that wasn't the book's last appearance, as it then made a cameo in a dream sequence during Agents of S.H.I.E.L.D Season 6. The Darkhold has had a more varied Marvel career than most actors could dream of.
In the comics, the Darkhold has covered even more ground. It burned at the stake with a heretical monk in the 12th century only to reform itself and wind up in the Vatican by the 17th century. Dracula hired a thief to steal it, but the Italian adventurer Cagliostro killed the thief and claimed the magic book for himself. Multiple pages of the Darkhold are also under the possession of cults called Darkholders, who use its power to worship Chthon, which is basically Marvel's version of Cthulu.
What the Darkhold means for WandaVision
Its inclusion in WandaVision makes perfect sense if you know the history of Agatha Harkness. Originally introduced to just be the Fantastic Four's babysitter, Agatha revealed herself to be an old-school Salem-style witch. Later in her Marvel Comics career, she became the mentor of the Scarlet Witch (aka, Wanda), and erased her memory after her twin boys, Tommy and Billy, were absorbed by Mephisto — this ultimately led to Wanda's mental breakdown in the House of M comics arc that WandaVision seems to be riffing on.
In the comics, Agatha Harkness never interacted directly with the Darkhold, so it's tough to say exactly what she plans to do with it. She has appeared in the Marvel comics series Darkhold: Pages from the Book of Sins, but that didn't involve her using the book, just knowing about it, which makes sense due to her witchy powers.
If Agatha truly is behind it "all along" using the Darkhold to amplify her powers, it's only a matter of time before the illusion is erased and Wanda loses her twins. Luckily, Agatha's comics past will give her a chance of redemption. She could erase Wanda's grief altogether, allowing her (and Marvel fans who only watch the movies) to carry on in the universe like nothing happened — at least for a little while.
The Darkhold might also be the key to defeating Agatha. After all, if this book can be used to banish a powerful witch like Morgan le Fay, it should work on Harkness too, right?