Kathryn Hahn paid a virtual visit to “The Tonight Show” on Friday, and discussed her recent role as wicked sorceress Agatha Harkness on “WandaVision”.

One of the most unexpected outcomes from the role was when her sitcom theme song “Agatha All Along” (a clever plot device revealing that her sitcom character Agnes was actually Agatha, and had been secretly pulling the strings behind the scenes) was released on iTunes and wound up hitting #1 on the charts, even topping Justin Bieber and The Weeknd.

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“I was like, ‘What is happening?’ I mean — the Biebs! I’m sorry Biebs, I can’t help you,” she joked to host Jimmy Fallon.

Despite being a formidable Marvel supervillain, Hahn admitted that still wasn’t enough to impress her children.

“They’re teenagers and pre-teenagers so I’m never gonna be cool,” she said.

Fallon, however, showed off a note that her daughter had written to her congratulating her after the “WandaVision” finale, telling Hahn that she’s a “bad-a**.”

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“It was very cute, language aside,” Hahn admitted. “In that letter, it was appropriate.”

In another segment, Hahn and Fallon play “Emotional Interview,” in which they both adjust their moods on the spot to reflect instructions they’re given, such as “way too positive,” “bad at lying” and “keeps saying ‘it is what it is.'”