Don't go fishing for details from Charlie Day about the Super Mario Bros. movie because he doesn't know much more than just what his own character has to say. Previously, it had been announced that Day, who's best known for his role in the long-running comedy series It's Always Sunny in Philadelphia, would be providing the voice of Luigi in the animated film. It was also announced that the movie would be releasing in December of this year.

Day addressed his casting in the Mario movie during a recent appearance on Jimmy Kimmel Live. He was not able to provide any kind of a fruitful update on the project, as he admits he knows nothing about it. Nintendo and Illumination are keeping such a tight lid on the movie's details that all they've really told Day was the lines that he needed to speak for his character. Here's how Day explained it to Jimmy Kimmel:

"I'm playing Luigi. In fact, I just was recording that this morning and I'd love to tell you all about it, but they are top secret with that stuff. Absolutely, this is serious stuff! I know nothing. I show up, and they're like, 'You say this and you say that.' And it's all funny and good, and then I walk out and there's like, two guys in overalls with hammers, and they're like, 'Don't you tell nobody about this Charlie!' ... Mario's probably in the know, but they don't tell Luigi anything."

Chris Pratt will be co-starring in the film as the voice of Luigi's brother Mario, though the actors didn't record their lines together. There had been some initial backlash to Pratt's casting when it was first announced, as he doesn't come from an Italian background. Producer Chris Meledandri has since responded by saying that Pratt is doing great with his voice performance, though Day's casting as Luigi still acknowledges the traditional Italian background of the Mario brothers.

“All I can tell you is the voice that he’s doing for us, and Mario, is phenomenal,” the producer said, per TooFab. “Yeah I can’t wait for people to hear it. As an Italian American myself, I understand. You know, I understand the comments. Charlie Day, who’s playing Luigi, actually comes from Italian heritage. Yeah, so that’s our nod.”

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A full cast list for Super Mario Bros. has been revealed, and it's a strong ensemble. This includes Chris Pratt (Guardians of the Galaxy) as Mario, Anya Taylor-Joy (The Queen's Gambit) as Peach, Charlie Day (It's Alway Sunny in Philadelphia) as Luigi, Jack Black (Jumanji franchise) as Bowser, Keegan-Michael Key (Key & Peele) as Toad, Seth Rogen (Pineapple Express) as Donkey Kong, Fred Armisen (Portlandia) as Cranky Kong, Kevin Michael Richardson (Teen Titans) as Kamek, and Sebastian Maniscalco (The Irishman) as Foreman Spike.

"It's an ambitious task," Meledandri has also said of bringing Mario back to life on the big screen. "The challenge is taking things that are so thin in their original form and finding depth that doesn't compromise what generations of fans love about Mario, but also feels organic to the iconography and can support a three-act structure."

Super Mario Bros. is scheduled to be released in theaters on Dec. 21, 2022.