With so much going on in the new trailer for WandaVision it can be hard to appreciate the potentially major impact of minor details. The leading theory about WandaVision's setup is that the Scarlet Witch, grief-stricken following the death of her significant other, Vision, creates a pocket reality where the two live happily ever after in a sitcom-perfect life. But the return of Vision would mark the return of one of the universe's most powerful weapons: the Mind Stone.
Vision's origins are intrinsically linked to the Mind Stone, as depicted in the film Avengers: Age of Ultron. When the Avengers originally retrieved the Mind Stone from Baron von Strucker, they discovered a consciousness within it, leading to ill-fated experiments that created the maniacal robot, Ultron. Ultron wished to create a perfect life form, but the fusion of the Mind Stone and the JARVIS artificial intelligence resulted in the heroic Vision, who helped put an end to Ultron's deeds once and for all.
Vision then met his own end in Avengers: Infinity War, when Thanos' quest for the Infinity Stones led him to pull the Mind Stone out of Vision's head, killing him. It was Vision's second death in a matter of moments as Wanda attempted to destroy the Stone shortly before Thanos used the Time Stone to undo her actions and retrieve the intact Mind Stone for himself. The trauma from this event is likely the inciting incident for Wanda's declining mental state, leading to the theory that WandaVision's sitcom-inspired setting is a Wanda-created pocket reality.
Yet Vision seems to act independently of Wanda in the new trailer, which shows both characters seemingly puzzled about their true history together and feeling displaced in the shifting dreamscape around them. Vision even comes across a startling revelation totally absent of Wanda when the character played by Kathryn Hahn informs him he's dead. The moment seems to indicate Vision may have been brought back to life. This could mean that rather than a pocket reality, the events of the show occur in a secluded portion of the reality Wanda is shaping around her. And if she brought back Vision, it appears she brought back the Mind Stone as well.
The gem sits in Vision's forehead just as surely as it ever did. The Mind Stone and Vision were inextricably linked during his life, and the Stone even served as a common basis for the couple's relationship. Wanda's powers resulted from Strucker's experiments with the Stone and the influence and effect Wanda and the Stone had on each other was the reason Wanda was one of the only people capable of destroying it in Infinity War. But this is not just some little memento of a relationship past that Wanda clings to -- it's an ancient artifact whose existence majorly affects the status quo of the universe itself.
Marvel previously confirmed the Infinity Stones are gone from the Marvel Cinematic Universe, although the Russo brothers, who directed Avengers: Endgame, theorized they still exist on some level given that Thanos only "reduced them to atoms" following the snap that wiped out half of all life. It could be that Scarlet Witch reassembled those scrambled atoms or that she formed a new Mind Stone from whole cloth with the sheer strength of her powers. Either way, there would be major consequences for the MCU if the Soul Stone was once again in existence. The couple's reunion may be give Scarlet Witch and Vision a few moments of bliss, but the stakes are too high for their ever after to stay happy for long.
WandaVision stars Elizabeth Olsen as 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. The limited series will debut on Disney+, though it does not currently have a release date.