Kathryn Hahn says she 'would not be surprised' if Mephisto appears in future MCU projects

• Kathryn Hahn said she "would not be surprised" if Mephisto was involved in "WandaVision."
• Hahn told Insider that she has "zero idea" if Mephisto will feature in the MCU going forward.
• Warning: Spoilers ahead for "Wandavision."

In a new interview with Insider, Agatha Harkness actress Kathryn Hahn addressed one of the most popular fan theories to emerge from "WandaVision" - the presence of Mephisto.

Hahn was speaking to Insider about her partnership with cleaning brand 9 Elements, "a line of laundry and home care products with vinegar and plant-based ingredients that are super-charged by science."

Hahn spoke to Insider about the partnership as well as her starring role in "WandaVision" and the possibility of Mephisto joining the MCU.

Mephisto is Marvel's answer to the devil - he's the big, bad ruler of the hell dimension who often, in the comics, makes shady deals with superheroes. He even had a run-in with Wanda herself in the comics, and Wanda used Mephisto to make her children. It's no surprise, then, that his involvement in "WandaVision" was speculated throughout, although that never came to fruition.

Hahn told Insider that she has "zero idea" if Mephisto will indeed be featured in the MCU at some point, but she did call Mephisto a "fabulous character."

"I would not be surprised by anything," Hahn said when asked if Mephisto could have been involved in the events of "WandaVision" or will be involved in the future of the MCU.

The actress continued: "The thing about these comics is that there's a nonstop bottomless pit of amazing characters."

Throughout the Disney Plus show's run, fans speculated that Mephisto was involved in the Westview shenanigans caused by Wanda. Ultimately, that didn't play out, with Hahn's Agatha Harkness revealed to be the overarching villain of the show instead.

However, even after the season finale, there are still some who believe that Mephisto was being teased throughout the show and possibly being set up for a future MCU appearance.

One of the potential teases came in the finale, when a billboard behind Agatha advertised a cleaning product that uses "the power of mother Earth." In the top right-hand corner, the billboard reads: "Available at your local M&B hardware store."

Many hardware stores use father-son names in the style of "John Smith and son," and the M&B in this instance could stand for Marvel comics' villainous father and son duo Mephisto and Blackheart.

This is one of many Easter eggs that were spotted throughout the course of the inaugural MCU Disney Plus TV show, and Hahn said that a lot of them came as "a surprise" to her despite being given the full scripts for the entire show.

"I'd read them of course, in the scripts, but I didn't quite connect them until after and when I watched them, I just thought there were so brilliantly baked in - so perfectly. So a lot of those were definitely surprises, the commercials were surprises," Hahn said.

It's interesting Hahn was given the entire script as previous MCU actors, like Spider-Man actor Tom Holland, have only been given parts of the screenplay in which their character features, and nothing more. But Hahn told Insider that the core cast - Paul Bettany, Elizabeth Olsen, Teyonah Parris - were given the entire script because the show was "such a puzzle."

"I think of the core actors definitely had to know their art because it was such a puzzle, which was very helpful, but there was a lot of tongue biting that had to happen for a very long time [to avoid spoilers and leaks], which was very difficult," Hahn said. "My children knew [of Agatha's big reveal] - hats off to them for keeping secrets for so long!"