WandaVision's Episode 6 may have revealed (among other things) the Marvel Cinematic Universe's very first confirmed mutant. while the word "mutant" still hasn't been used in the MCU (yet), WandaVision's new "An All-New Halloween Spooktacular!" episode pretty much tells us that one character on the show is actively undergoing mutation before our eyes. (Spoilers Follow) That character is none other than Monica Rambeau (Teyonah Parris). Monica is working with Jimmy Wood (Randall Park) and Darcy Lewis (Kat Dennings) to circumvent SWORD director Hayward, which leads to Darcy hacking Hayward's computer. There, Darcy discovers Monica's medical files, which depict the truth about what's happened to her since passing through Wanda's barrier.
As Darcy deciphers, Wanda's Hex barrier isn't just making cosmetic changes to reality, like clothing; after passing through the barrier, Monica's very cellular structure is being re-arranged.
The key seems to be repetition: Monica passed through the barrier twice, The first time, Monica was pulled into the barrier when she first investigated Westview along with Jimmy Woo; the second time, Wanda expelled Monica from her bubble, throwing her out of the barrier. Now, Darcy warns that a third pass through could affect Monica in unpredictable and drastic ways - but Monica is still committed to going in and helping Wanda, no matter the costs. This is a clear lead-in to Monica Rambeau's comic book legacy of becoming the energy-manipulating hero Photon.
The end of WandaVision Episode 6 showed Wanda expand the scope of her reality-altering bubble exponentially, with little signs that it will stop before enveloping the entire MCU. With theories going strong that WandaVision is pulling a "Reverse House of M" (wherein Wanda creates a new reality full of mutants), this could be a key first tease of how that franchise-altering process would happen.
At the same time, Marvel Comics die-hards will be quick to point out that a "mutant" is not something that can be created by an event like Monica going through cellular alteration. Superpowered individuals who gain their powers through magic, science, or cosmic influences are typically referred to as "Mutates" in Marvel lore. Mutants, by comparison, are unique in that they are born with the powers that they have.
Of course, Marvel Studios may simplify the distinctions between the two concepts for the MCU mainstream audience. While Monica Rambeau's comic origin has "interdimensional energy" as the source of her powers, MCU fans typically need more concrete explanations. Expanding the term "mutant" to anyone born with gifts and survivors of strange phenomenon/experiments, you get a better, more uniform term than "enhanced" that can cover the X-Men and other heroes alike.0comments
There is also another option:
In some key instances, Marvel's mutants don't manifest their powers during the natural pubescent maturation process, they have their powers unlocked or catalyze by experiments or traumatic events. This is one theory about Wanda Maximoff's MCU version: she was always a mutant, and the Mind Stone simply helped her and Pietro/Quicksilver tap into her gifts. The same could arguably be true of Monica.