Spoilers for Disney+ series WandaVision follow

Kathryn Hahn has opened up on playing a crucial character in MCU phase four series WandaVision, streaming on Disney+.

Seemingly set in an alternate reality where Wanda Maximoff aka Scarlet Witch (Elizabeth Olsen) and Vision (Paul Bettany) live through different television eras, the series is onto a much darker path in its final episodes.

A study on grief and trauma, WandaVision also surprised viewers with a big twist about Hahn’s character, Wanda’s nosy neighbor Agnes. Despite her friendly demeanor in the first few episodes, Agnes is revealed to be none other than powerful, evil witch Agatha Harkness.

Kathryn Hahn Needed A Marvel Crash Course Before Playing Agnes

The actress admitted not to be very Marvel-savvy before playing Agnes aka Agatha on WandaVision.

“I was able to do a deep dive on Agatha Harkness, but I definitely needed a little bit of help with the Avengers and going backwards,” Hahn told Seth Meyers.

"Because it was a little bit of a word salad, walking into this. I couldn’t remember who is who and what was what,” she added.

Hahn said that her son "was a huge, huge help.”

Her son also had a helpful prop to get his mom set-ready: the Infinity Gauntlet.

“We’ve put on gems that we have had to re-hot-glue a few times,” Hahn said.

The gauntlet belongs to Hahn’s son, who seems to be the resident Marvel expert of the family.

“This was an item of great reverence in my house in my son’s room for a very long time,” she continued.

“Not anymore, he wants to make sure everybody knows,” she added.

Related: '50 Shades' Star Jamie Dornan Shares How He Kept It Together In 'Barb & Star'

Hahn On The Last Episode Of ‘WandaVision’

Hahn also revealed how she first found out about the big twist concerning her character.

Like in the song Agatha All Along topping the iTunes chart, Hahn had always known her character Agnes wasn’t all smiles. The series’ creators had filled her in on Agatha’s role from the start.

“I walked in, I was led into a conference room… […] It was very, very inner world,” Hahn said.

“And then you opened the door to this conference room and they had all over the walls like, the entire story,” she said.

WandaVision will air its ninth and final episode this Friday and Hahn thinks the conclusion will make fans happy.

“I thinks it’s gonna be very satisfying,” Hahn said.

WandaVision is streaming on Disney+

Next: Eve Hewson Talks Getting Into Character For Netflix Thriller Sensation 'Behind Her Eyes'