Emma Corrin didn’t need big muscles or a black belt in karate to be Marvel’s next big supervillain. Just a bald noggin and creepy fingers.

In “Deadpool & Wolverine,” the Golden Globe-winning British actor gives Ryan Reynolds’ Deadpool and Hugh Jackman’s Wolverine fits as formidable telepath Cassandra Nova, literally digging into their brains with her digits. The heroes run afoul of Cassandra when they’re banished to the Void, a purgatory wasteland she rules alongside her henchmen, and she’s the key to them escaping the hellish place.

After playing Princess Diana in “The Crown” and Gen Z hacker/detective Darby Hart in “A Murder at the End of the World,” Corrin reveled in being evil for a change. “The twinkle in her eye and the flippancy in which she sort of destroys people and feels whatever, that's really fun,” says Corrin, who identifies as nonbinary and uses they/them pronouns.

Join our Watch Party!Sign up to receive USA TODAY's movie and TV recommendations right in your inbox

It’s Cassandra’s (and Corrin’s) MCU debut, but she’s related to an icon from Fox's Marvel superhero movies. In the comic books and the new film, she’s the twin sister of Charles Xavier, leader of the X-Men, who has been played over the years by Patrick Stewart first and then James McAvoy. And like her brother, Cassandra’s an Omega-level mutant who, with just a simple gesture, can rip your skin off and leave you in a heap of bones and viscera if you insult her.

Need a break? Play the USA TODAY Daily Crossword Puzzle.

Director Shawn Levy loved the character’s complicated relationship with her sibling “and how that would lead Cassandra to a unique fascination with Wolverine,” he says. “She has issues with the world (and) her brother, and she would know the special relationship between Wolverine and Professor X: What would that trigger in her? That was rich fodder for storytelling.”

And Corrin was the ideal Cassandra because they come in “with no preestablished, predictable persona,” the filmmaker adds. “I liked Emma's fluidity as a performer, the fact that Emma can play charming and pithy and then on a dime shift to something much darker and more nefarious.”

Since Wolverine and Deadpool are “very physical presences,” Corrin says, “to have the villain try and match that would be almost too much of the same thing.” So while Cassandra’s hugely powerful, “she doesn't need to perform it for people, and there's kind of more power that way. She's very chill. She comes across very relaxed, and then the weather changes and you can see the extent of her power, and I think that will be maybe quite refreshing.”

When first cast, Corrin wondered if they needed a personal trainer to get in shape the Marvel way. “I was like: 'OK, great. I'm going to get fight training, stunts, finally master Taekwondo,’ ” Corrin says. “They were like, ‘No, no, you have purely powers of telepathy.’ And I was like: ‘Are you kidding? This is my entry into this universe?’ “ But instead, they found having only their head and fingers to fight with “kind of the greatest challenge ever.”

Corrin got a buzz cut and was outfitted with a bald cap to match the Mr. Clean look of Xavier. Plus they had prosthetics put on their fingers that added a few inches of extra weirdness when Cassandra is messing with a person’s head.

But wearing those, “I just couldn't do anything,” Corrin says. “I couldn't be on my phone, which was great for my screen time but terrible for going to the bathroom because I could never go alone. I always needed someone to help me because I couldn't touch anything.

"It was kind of hell but very interesting."