The following contains major spoilers for Doctor Strange in the Multiverse of Madness, now in theaters.
WandaVision proved to be the antecedent to Doctor Strange in the Multiverse of Madness that many expected, though with diverging opinions of success, as the Scarlet Witch became consumed by reuniting with the children she brought into existence while enslaving the town of Westview. Wanda's grief over the death of Vision led her to construct a reality where the two lived happily ever after, populated by real people who were forced into set-piece archetypes to fulfill the needs of her fantasy. Her fairy tale also included a pair of twin boys that she and Vision hastily raised into magical adolescence during the few weeks of the town's enforced captivity. Creatures of conjuration, Billy and Tommy became linchpins of Wanda's fragile psyche and identity.
In the aftermath of the Westview Event, endowed with a true understanding of her own reality-bending powers thanks to Agatha Harkness, Wanda came into possession of the Darkhold. The book of almost infinite dark power with spells that could enable contact between parallel dimensions, Wanda discovered that she was a mother to the same two boys in almost every other reality. Consumed by the loss of her children, she endeavored to infiltrate one of these alternate worlds and replace their mother with herself in a selfish and grisly act of potentially traumatic self-murder. However, an episode of Rick and Morty offered up a more graceful alternative than Wanda ever seemed to consider.
After becoming aware of America Chavez's singular ability to traverse the multiversal superhighways, Wanda sought to capture the young woman and drain her of her powers. The ritual would leave America dead, but it would give Wanda her abilities in full, enabling her to travel to any multiple reality of her choosing with much more precision than America could execute purposefully. Lacking the access to punching interdimensional portals into being, Wanda's only transit to homologous universes is through an ability known as Dream Walking. Its effects are temporary; it leaves one's original form unprotected in a deep trance to maintain the connection and can only be achieved using a variant of oneself as a conduit.
Wanda intended to use this power so that she could replace a version of herself and step into her life while retaining the ability to reset or solve any future problem with America's stolen star gates. When Strange confronted Wanda with the depravity of her plan, killing the mother of the children that she would hope to raise, she dismissed his concern completely. Wanda had come to a place of complete peace when it came to killing whoever she needed to kill to see her plan come to fruition, including her own variant. On Earth C-137, a pair of portal users considered another solution. There may be no show that has ever so thoroughly addressed the concept of the multiverse than Justin Roiland's and Dan Harmon's twisted family adventure of a drunken super scientist drowning in self-loathing ennui and his often obliviously irresponsible grandson, casually toppling empires and engaging in cosmic hedonism.
Very loosely based on Doc and Marty from Back to the Future, Rick and Morty once engaged in a mishap that left every human being in their world a disfigured lump of random limbs and oozing flesh in Season One's "Rick Potion No. 9." After all attempts at curing them failed, Rick opted to simply transport them to a universe where they died and teleported into the lives they left in their wake at the moment of their death. They buried the bodies in the backyard and went about their days as if they were the Rick and Morty that their family, friends, classmates and colleagues had always known. There was no fight to the death; no need to feel responsible for the demise of their doppelgangers, only the fractured peace of knowing they left one world in ruin and entered another with a fresh start.
The nature of Wanda's children leaves a lot of unanswered questions as to how they came about and, subsequently, whether her plan could ever have worked or if the Rick and Morty option was ever a viable one. The children were spell born in the 616 continuity, so it stands to reason that they were also magically manufactured in the other timelines as well and perhaps as a result of similar grief stricken responses. In the 838 reality, Vision seems to be absent, just as he is in the Sacred Timeline, which may mean that killing Wanda in that reality might result in the cessation of the witchcraft that allowed for the boy's existence.
The Marvel Cinematic Universe also staked a claim on the nature of dreams themselves, establishing that any dream that includes the presence of the person dreaming is almost certainly someone experiencing the life of a variant glimpsed through the thin curtain of REM sleep. In that light, it is possible that Billy and Tommy were real in every other universe, born in some way from a non-arcane source, and that their identity in the 616 universe was influenced by their natural existence in parallel worlds. This would suggest that the Wanda of the MCU did not conjure them out of anything but formed them from the leaking essence of her shared experiences across multiple realities.
Given that Wanda had presumably spent a lot of time scouring these mirrored planes of existence, enough to conclude that she was a mother in every version of them except for her own, implied that she would have been aware that killing her alternate would amount to a self-defeating act since it would mean the death of the children she hoped to raise. This may indicate that the tethers of witchery did not connect Wanda and her children in other realms, which would mean that her plan was viable and that the Rick and Morty option was also on the table. Given how powerful Wanda is in any reality, though, it may have been the reason why her death was a rarity in all the infinite universes that she could not rely upon.
To see Wanda scar her potential kids unnecessarily, Doctor Strange in the Multiverse of Madness is now playing in theaters.