Though The Lego Movie 2: The Second Part shares the characters, cast, and universe of the 2014 original, two things that didn’t hold over were directors Phil Lord and Chris Miller (who jumped over to Spider-Man: Into the Spider-Verse). Though Lord and Miller stayed on as writers and producers, Mike Mitchell (Trolls, Sky High) inherited the Lego-verse with an eye towards keeping it as vast, frantic, and beloved as in the first movie.

Mitchell also inherited the limitless character possibilities that could make brief appearances in Lego form. Limited only by their imaginations (and whatever Warner Bros. legal thought was kosher), The Lego Movie 2 once again packs the story with cameos, obvious and out-there.

We talked to Mitchell about carrying on the Lego legacy, getting to play with just how the world ticks, and all the kooky characters the Lego world has to offer.

[Ed. note: This article contains spoilers for both 2014’s The Lego Movie and The Lego Movie 2: The Second Part.]

Polygon: The first Lego movie ends with the big reveal that the movie is taking place in our world, and these Lego characters are actually toys. How do you build on that reveal?

Mike Mitchell: It was a pretty big challenge because the first movie was so special and it was such a surprise when it got to that live-action bit. So much so that when Chris and Phil first approached me, I was like, I’m not so sure you guys should make a sequel because I loved that first Lego film so much. Then they pitched me this idea that actually went even further than just a little boy and his father down in the basement. And I was like, oh now I need to be a part of this film — that’s an amazing idea. I can’t wait to work on it and I can’t wait to figure out who this little sister is. It really started from how do we go further and make a worthy sequel considering the first one was so great.

How did you differentiate between Finn playing with his Legos and Bianca playing with hers?

It’s really neat because the little boy, that cute little kid from the first Lego film, is actually the exact same actor that we got to play in this film! He really is that kid grown up and now he’s a teenager. He was the perfect age that we wanted them to be, to tell the story about how he’s getting older. Everything has to be rough and dusty and cool, like in that apocalyptic world. Everything he plays with is rusty and has spikes. He’s almost getting to that age where you kind of isolate yourself. Maybe he’s gonna stop playing with Lego and he’s going to turn his back on being a child and [being] so open like the character of Emmet is. That was a really interesting challenge to explore a kid who’s still playing but becoming too cool for school to play.

On the other hand, that little girl that shows up at the very end of the first film we introduce her at that age and she’s grown up. So how is she involved with her play? We decided we that she was into space travel and she’s very musical and really crafty. She has way less rules than her brother has when he plays. So she incorporates all sorts of different Lego together from the minifigs to the Duplo to the Friends dolls. And then because she’s crafty, she incorporates glitter and fabric and pipe cleaners. She’s super duper creative. It was a challenge, but it’s a really fun challenge to leave that basement and go up into an entire universe created by this little 7-year-old girl.

How do you decide which characters and real-life people make appearances?

I’ve never worked on a film before where you can like pull characters from other worlds into this world and they actually fit. Like, it was bizarre — why wouldn’t Ruth Bader Ginsburg and Bruce Willis be in the same movie together? It was really just whatever made us laugh and whatever we thought was interesting. At one point the whole cast of the Wizard of Oz shows up for a second. Certainly we wanted to take advantage of any Harry Potter characters or Lord of the Rings characters. The whole Justice League shows up. And it’s also weird that Batman who’s played by Will Arnett. His character is the only Batman from all the Batman films that’s actually aware that there are other Batmen in other films. It’s such a weird world, a weird universe that these Lego Movies have created where there’s almost no rules at all.

Can you tell me a bit more about involving Aquaman and the rest of the Justice League?

We did a little short film for San Diego Comic-Con with Emmet and Batman and Lucy (WyldStyle), and we thought it’d be fun since the Aquaman movie was coming out that Jason [Momoa] come in and do the voice for Aquaman. He was so game to, like, poke fun of himself, and created this whole character. That’s when we first said, you know what, we’ve got to have this character in the film. So we told his character and he was more than happy to do the voice.

We also inherited Channing Tatum as Superman and Jonah Hill as Green Lantern. We thought it’d be great to have them come back again. They have a contentious relationship where Green Lantern needs to be friends with Superman. We gave an arc to that little story, where when the little sister plays with those characters, she doesn’t know the rules of the superhero world. In fact, Lex Luthor and Superman are best friends when she plays with them. She doesn’t mind having three Wonder Women show up at one time. That’s not strange for her at all. But for someone like Emmet who represents a little boy, it blows his mind that there’s no rules.

How did you decide to have Batman get married in this movie?

Well, one, we thought it was really strange that Batman would fall in love with just a handful of bricks that shapeshift into anything. I don’t know what that says about Batman, but it was also interesting ... Batman is convinced he’s the leader of any scenario he’s in. Queen Wa’Nabi is the leader. So they do already have a lot in common. They both live in huge mansions and they both have snooty butlers as their assistants. I guess there’s a lot of common ground between those two and they’re both a little bit lonely. I guess by accident who knew, but it was a match made in heaven.

One of the best cameos was Bruce Willis’s appearance climbing through the air ducts — and he voices himself! How did that come about?

In these movies when they’re on a mission, it seems like every mission has characters crawling through air conditioning ducts. And so once we created that sequence where like, we’re all huge fans of Die Hard and John McClane, so we’re like, let’s ask Bruce Willis. And so we went to him and we’re like, “Hey Bruce, if you wouldn’t mind, we’re going to suggest that your character is defensive and might very well just live in the air ducts of the world.” And Bruce was like, “Yeah, I get it. Let’s do it. Great. Let’s go.” And so he was, he was as game as Jason was to poke fun of themselves.