Wandavision, the first of the planned Marvel Cinematic Universe television series set to air on the streaming service Disney Plus, has currently aired four episodes up to this point and even some of the characters on it are beginning to think that the lead character, Wanda Maximoff is up to some mischief. Ahead, this entire article will be purely my own speculation based on what we have seen. What we know up to this point is that Wanda and Vision are stuck inside some sort of alternate reality in a made up town. Monica Rambeau, a SWORD agent, who had been expelled from the reality came to and said it was all Wanda. This has led a lot of people to believe that Wanda may have gone on some sort of mental break and in a fit of rage she created this reality where she got the chance to live the perfect life with her love, Vision. Most of that working theory tracks as there are instances of it happening in the comics, like the House of M storyline. I don't believe that Marvel is going that direction with the character just yet, I do believe that she helped create this reality, but is not going bad, instead she's under a spell. We've been told before the show had aired that the events of Wandavision would lead directly into that of the Doctor Strange sequel named the Multiverse of Madness and that the two would share a villain. It is possible that villain is indeed turning out to be that of Wanda, but it does not make sense when her character has always wanted to be accepted. Through all of her loss, she still would want a sense of belonging on some level from people and not turn on them completely.
Wanda and Vision have always had a special relationship ever since they met, and even more so considering her powers and Vision's genesis. During a difficult time and the loss of her only remaining family member, Pietro, Vision was always there for her. So was Steve Rogers and the Avengers, essentially forming a surrogate family for her. What I believe to truly have happened is that some time after the events of Avengers: Endgame after the dust had settled (poor joke I know) and Tony's body had been put to rest, Wanda took inventory on what she had. Vision was gone, her close friend in Steve was now an old man and couldn't lean into him nor could she speak with the now deceased Natasha Romanoff. At a certain point, she decides to go to SHIELD headquarters where presumably the corpse of Vision had remained. Through her burgeoning powers after coming back from the snap, and her emotions being erratic she attempted to bring him back to life. In doing so, she took everyone inside into some sort of warped television reality. However, Vision still was not alive. In order to bring him back in some way, she'd need help from that of someone stronger and much more dangerous.
Friendly Neigborhood Witch
In the third episode, Vision had found his neighbor Ralph speaking with Agnes Harkness and both of them looked concerned. Agnes was downright terrified at one point. All of this took place when Wanda was losing control of her powers so it stands to reason that her spell on the citizens of Westview began to fade ever so slightly allowing them to understand what was happening. The same even took place in the second episode when Wanda heard a voice calling to her through the radio asking her, "Wanda, who is doing this to you?" Another clue would stem from the first two episodes in which the townspeople all seem to be encouraging Wanda and Vision to procreate, in fact anytime the words "For the Children" the others would repeat in such a way that it mirrored that of a cult reciting something like a prayer. All these tiny clues begin to add up to the possibility that someone is pulling Wanda's strings. Looking to the comics, you can find that Agnes Harkness may in fact be a part of this ordeal. In the comics there was a witch named Agatha Harkness who was a mentor to Wanda and taught her real magic. Agnes seems to even have the same brooch in every episode so far that looks oddly similar to the same brooch that Agatha wears in the comics, so i do believe that the two are one in that same. The two, in the comics, would become enemies and Wanda killed Agatha, doing so ended up having horrible implications. After being killed, she resurfaced later on and at this time Wanda's two infant children began to exhibit odd behavior, Vision had dismantled and Agatha had no reason for her strange revival. In truth she was in cahoots with Mephisto and in using Wanda, they were able to store fragments of Mephisto's soul into Wanda's children giving them life. Mephisto absorbed the children, and in doing so sent Wanda into a horrible rage which Agatha tried to help by wiping her memory, saving her the trauma. I could see how Marvel could be roughly using this story line to help set up a major villain for the future of their grand scheme. The mysterious and accelerated birth of Billy and Tommy can be explained by the nefarious Mephisto's presence as well as Agnes' role.
The Devil is in the Details
Mephisto's scheming would fill in a lot of holes. Vision being dead, and now seemingly alive could be explained as Mephisto offering to bring Vision back to life in return for something he would want later down the road. In Wanda's weakened emotional state, Mephisto could have made this deal with her, not knowing she'd be giving up her unborn children. The other factor in all of this is how this series could help set up future story lines in two upcoming Marvel films. Kevin Feige had teased that after Endgame it is highly unlikely that we'd see a ten year narrative arc that would be as big and expansive as that of the Infinity Stones and Thanos. Instead they would be opting to smaller and more concise story arcs. The introduction of Mephisto and Wanda loosing herself to a horrible tragedy could explain the destruction of reality allowing multiple universes to converge into one. This would easily lead into the Multiverse of Madness and Spiderman 3, making a self contained "3 movie" story. Wanda's loss of Vision and her children due to the deception of Mephisto would also urge Doctor Strange to go ahead and teach Wanda how to better control her emotions as well as her magic. In fact, I would not be surprised to see the Doctor himself before the end of the season. I've also seen mention of Nightmare as a possible villain amongst Wandavision fans. It has merit as the previous director of Doctor Strange 2 desperately wanted to use Nightmare as the villain which Marvel seemed to push back against. With Scott Derrickson moved on from the project, it doesn't seem likely that Nightmare would be present in that film which then would rule him out of Wandavision. I could see the merit in the thought as when Monica Rambeau was expelled from Wanda's reality inside Westview, she seemed to wake up. Nightmare could have the entire town asleep in some horribly warped dream and absorbing Wanda's power. All of this seems like a stretch as it's more likely when Rambeau was thrown out of Westview that the sheer force of the spell knocked her out briefly. Mephisto and Agnes seem to be the most likely culprit of what is behind this oddly entertaining series.