WARNING: The following contains spoilers for WandaVision Episode 5, "On a Very Special Episode...," now streaming on Disney+.
The last two episodes of WandaVision asked who's controlling Westview. Although Monica Rambeau, S.W.O.R.D. and now Vision believe that Wanda is in control, Wanda insists she's not. She may have said this just to placate Vision, but this doesn't explain why she couldn't remember their origins in Episode 1 or why she was surprised by her brother's sudden arrival at the end of Episode 5. Wanda could've only recently become aware of what's going on or perhaps she isn't the only person who can control Westview.
Many fans suspect that Wanda and Vision's neighbor, Agnes, is Agatha Harkness, an ancient, powerful witch who mentored Wanda in the comics. While this has yet to be confirmed in the show, Vision has noticed that Agnes has a way of showing up at the most opportune times, and she wasn't fazed by the twins' rapid aging. More importantly, S.W.O.R.D. has not been able to identify her or her absent husband, Ralph, on screen. If anyone is controlling Westview aside from Wanda, it's probably Agnes.
Some may argue that Agnes is playing the part that Wanda created for her like the rest of Westview, but she's always there with whatever Wanda needs. She brought over groceries so Wanda could make dinner for the Harts, she lent her pet rabbit to Wanda and Vision for their magic act, and she showed up twice in the last episode when Wanda's family was in need of something.
The only big event she wasn't a part of was the twins' birth, which was handled entirely by Monica. Immediately after, Agnes tried to turn Vision against Monica without revealing too much. Perhaps Agnes originally intended to be the one to deliver Wanda's children, but she didn't account for an outsider taking her place. Additionally, it seems like she recruited Herb to help spy on the couple. In short, she's a much more active participant than the rest of the neighbors.
Unlike most of the neighbors, Agnes seems to have a deeper understanding of what's going on in Westview. Not only did she recognize Monica as an outsider, but she also stopped Herb from revealing too much to Vision. More recently, she broke the illusion by asking Wanda if they should, "take it from the top," like an actor who had forgot their lines. Even if she was taking her cues from Wanda, this was an odd decision given how much of a tip off it was for Vision.
Either Agnes slipped up or she changed her mind about keeping Vision in the dark. This might explain a certain scene from the first trailer, which hasn't aired in the show yet. In the scene, Vision breaks Agnes out of a trance, and she tells him that he's dead. It's unclear what her motives are at this point, but it appears she's more comfortable being open with Vision.
In another big moment for Vision, the synthezoid "wakes up" his co-worker, Norm, who tells him, "You have to stop her. She's in my head," but he doesn't specify who "she" is. The obvious answer would be Wanda, a telepath, but it could also be Agnes. After all in the comics, Agatha's magic was strong enough to alter Wanda's memory and create illusions. If Agnes is the Marvel Cinematic Universe's Agatha, she could've been the one to create everyone's new backstories, and she could've made Wanda forget how her sitcom life in Westview started.
Later in Episode 5, Agnes explains that the twins' dog, Sparky, died after eating the poisonous leaves of her azaleas. The event is painted as an accident, but if Agnes is in control, there may be something far more nefarious going on. It has been implied that Wanda stole Vision's corpse from a S.W.O.R.D. facility and brought him back to life in Westview. If Agnes knows about this, she might have wondered if Wanda could resurrect organic beings as well, so she killed the dog to test this theory out, but Wanda doesn't bring Sparky back, despite Tommy and Billy thinking she can.
At the end of the episode, Wanda is shocked when an alternate version of her dead brother, Pietro, shows up on her doorstep. Considering Wanda's reluctance to resurrect Sparky and the fact that Agnes has been trying to fulfill all of Wanda's desires, perhaps the secret witch took it upon herself to bring Pietro to Westview after Wanda expressed to the twins that she missed him. If Agnes isn't able to raise the dead herself, she may have plucked him from another reality and changed his memories so he'd fit into Wanda's narrative. Whatever the case may be, Agnes could be up to something.
Written by Jac Schaeffer and directed by Matt Shakman, WandaVision stars Elizabeth Olsen as Wanda Maximoff/Scarlet Witch, Paul Bettany as Vision, Randall Park as Agent Jimmy Woo, Kat Dennings as Darcy Lewis, Teyonah Parris as Monica Rambeau and Kathryn Hahn as Agnes. New episodes air Fridays on Disney+.