Barbie is 23% larger than everything in Barbieland to mimic the awkward, disproportionate scale that real Barbies and Barbie activity sets are produced in. This is why Barbie sometimes appears too large for things like her car or why ceilings seem to be too low in the Dreamhouses.
According to Ryan Gosling, he accepted the role of Ken after seeing his daughter's Ken doll lying face down in the mud next to a squished lemon. He then took a shot of the doll and lemon and sent it to Greta Gerwig, saying, "I shall be your Ken, his story must be told."
Composer Mark Ronson wrote the song "I'm Just Ken" largely as a joke, and recorded a demo for Greta Gerwig not seriously expecting it to be included on the soundtrack. However she liked the song, and when she shared it with Ryan Gosling he felt so strongly that it added to the character of Ken he successfully advocated for it to be made a musical number in the film. Ronson remarked that he was amazed how much Gosling's interpretation of the song improved upon his original intent.
John Cena wanted badly to appear in the film, but could only take a small part due to scheduling conflicts with Fast X (2023). When he was offered the part of Ken Mermaid, he accepted it instantly, against the wishes of his agency, explaining, "[The agency is] just going on what they know. And what they know is, 'This entity, this commodity gravitates toward these things, we should stay in this lane.' But I'm not a commodity. I'm a human being, and I operate under the construct of every opportunity is an opportunity."
Michael Cera said his casting as Allan was "very last-minute," explaining, "I somehow got Greta's email address, I think through a common friend of ours, and I emailed her like, 'Can I be in it? Can I do that part?' And she was like, 'Let's get on a Zoom right now. Here's a Zoom link, I'll be on there for the next hour.' So she was just hanging out on the Zoom, like, 'Click the link whenever you're ready.' And then we talked about it, and it just all happened really fast from there."
Ann Roth: The older woman on the bench is played by an Oscar-winning costume designer, whose long and prolific career first started in the mid-1960s; upon the Barbie movie's release she was 91 years old. Though she was still actively working as a costume designer, she did not design the costumes for the Barbie movie, and this is her first credited movie role as an actress. Greta Gerwig refused to cut Roth's scene, holding her ground against studio executives by saying "I love that scene so much, and the older woman on the bench is the costume designer Ann Roth. She's a legend. It's a cul-de-sac of a moment, in a way - it doesn't lead anywhere. And in early cuts, looking at the movie, it was suggested, 'Well, you could cut it. And actually, the story would move on just the same.' And I said, 'If I cut the scene, I don't know what this movie is about.'"