Just saying the words "Lego Batman" is probably enough to bring a smile to your face. The character voiced by Will Arnett was the breakout scene-stealer in The Lego Movie, so the thought of him starring in his own film is both obvious and enticing.

Lego flicks like The Lego Batman Movie are extremely complex undertakings — even more so than your typical animated film. Animation is always a wildly complicated proposition, but when you add the rules, boundaries, and playful attitude of the Lego brand, things like casting, production, and visual effects require a new layer of attention to detail. The obstacles these filmmakers have to work around and the expectations of fans that must be met are a recipe for intense pressure.

Needless to say, the process of making these things is a fascinating one. Here are 15 amazing and surprising facts about The Lego Batman Movie (which, by the way, is a must-see) that you probably don't know.

15. The cast includes some big surprises

Mariah Carey as Mayor McCaskill in The Lego Batman Movie

You already know Will Arnett is the voice of Batman. And you probably know that Michael Cera stars as Robin and Rosario Dawson is playing Batgirl. You probably even know that Zach Galifianakis is the Joker.

But there are a bunch of famous names that you likely had no idea are in The Lego Batman Movie. For example, who do you think the filmmakers tapped to play the mayor of Gotham? If you weren't thinking Mariah Carey, then you'd be wrong. You may have heard that Billy Dee Williams voices Harvey Dent/Two-Face, reprising the role he first brought to life in Tim Burton's Batman. But you probably haven't heard who plays the Riddler: famed late-night talk show host Conan O'Brien.

Other names you'll recognize include Eddie Izzard, Seth Green, Flight of the Concords' Jemaine Clement, Trailer Park's Doug Benson, Zoe Kravitz, Unbreakable Kimmy Schmidt star Ellie Kemper, character actor Hector Elizondo, Brent Musburger, The Nerdist's Chris Hardwick, and more. The film certainly isn't hurting for star power.

14. Actors performed together

Will Arnett and Zach Galifianakis recording together for The Lego Batman Movie

It's a known practice in voice acting that actors come to work and record their lines alone. The director is there, guiding them with inflection and meaning, but other than sound/recording engineers, that's about it. So where's the rest of the cast? They all record solo. It's usually a scheduling thing; voice actors tend to have a lot of jobs going at once.

In The Lego Batman Movie, however, actors performed scenes together whenever possible. This was particularly used anytime someone was paired up with Will Arnett, so they could bounce ideas off of each other. That's right: the comedically-skilled actors in this movie were allowed to (gasp!) improvise dialogue.

Arnett and Zach Galifianakis riffed off of each other as Batman and Joker. Arnett and Dawson did the same as Bats and Barbara Gordon. When you've got a group of actors that are this good at being funny, the smart thing to do is put them behind a microphone and get out of the way.

13. The voice takes a serious toll on Arnett

Will Arnett as Batman in The Lego Batman Movie

Perhaps the most recognized aspect of Lego Batman as a character is Will Arnett's voice. Some fans have gone so far as to call it the definitive Batman voice.

It was the directors of the original Lego Movie, Phil Lord and Christopher Miller, who helped Arnett land on that deep, deep voice. In Lego Batman's press materials, Arnett is quoted as saying that he and the directors experimented for a while before they found the Caped Crusader's "sweet spot." They felt that taking the time to get it right was important, because this character would never work if he wasn't so utterly deadpan. "This is a guy who takes himself very seriously," says Arnett.

But that commitment to getting it right comes at a cost. Not since Andy Serkis croaked out Gollum's unique rasp has an actor suffered so much for a vocal performance. Arnett says he his voice is wrecked "after three or four hours" of recording.

12. Two actors sing on the soundtrack

Batman and Robin, who sing in The Lego Batman Movie

A total of four songs are listed in the movie's credits with performances or featured appearances by Arnett's Batman. These include "Man In the Mirror," the 1960s "Batman Theme," and "Bad Boys," all of which Batman undoubtedly sings at various humorous parts of the film. He's listed as featured on the original song "Friends Are Family," by Oh, Hush.

He's not the only one to get in on the action, though. Arnett's fellow Arrested Development alum Michael Cera has one of the standout performances in the film as the brightly-colored, happy-go-lucky Robin, aka the antithesis to Batman. Cera appears on three tracks, and from their titles, it's easy to guess that he too bursts into song from time to time, with tracks as diverse as "We Are Family," "It's Raining Men," and "Fly Robin Fly."

If that sounds like a lot, it's actually a small percentage of the soundtrack. A total of 28 songs are credited.

11. Zach Galifianakis took inspiration from a familiar source

Zach Galifianakis as The Joker in The Lego Batman Movie

The major underlying theme of The Lego Batman Movie is the Dark Knight's need for friends and family, despite his repeated desire to work alone. This is why the story is constructed so that several people in the movie — such as Robin and Batgirl — want to work with Batman, to help him. He has to overcome his destructive self-reliance.

This emotional arc extends even to the Joker, Batman's arch-nemesis. He may not want to be part of Batman's family, or even necessarily work with him, but this Clown Prince of Crime desperately wants to be acknowledged as the Caped Crusader's greatest foe. But of course, Batman refuses to give him the satisfaction.

Actor Zach Galifianakis, who voices the Joker, believes that the character deserves that validation. He feels that way at least in part because of how "unpredictable and wild and clever" Joker is — a characterization for which Galifianakis drew inspiration from Jack Nicholson's famed 1989 take on the role.

10. The director is a huge Batman nerd

Chris McKay, director of The Lego Batman Movie

Chris Miller and Phil Lord weren't available to follow up their directing of The Lego Movie this time around (they're busy working on the Han Solo anthology movie for Disney). So they brought in their editor and director of animation from The Lego Movie to take the reigns.

This marks Chris McKay's first big-screen credit as a director, but his resume includes more than just Legos. He directed and edited three seasons of Robot Chicken, as well as all three of that show's Star Wars specials. He also worked on a satirical cartoon called Moral Orel and the short-lived Titan Maximum on Cartoon Network.

It also just so happens that McKay is an enormous Batman fan. You need look no further than his right arm for proof, where he has a tattoo of Catwoman permanently inked. His fandom doesn't end with Batman, though. His left arm bears a tattoo of Captain America's shield!

9. The movie's look is intentionally different than The Lego Movie

Atmospheric lighting and smoke in The Lego Batman Movie

You'll notice a lot of similarities between the look and feel of The Lego Movie and The Lego Batman Movie. Both are films in which Lego Minifigures are alive, and both feature environments made completely out of Lego bricks. But if you take a closer look, you'll notice some striking differences.

Rather than slavishly follow the first film's structures, the filmmakers behind Lego Batman decided to look at what the unique world of Batman required, and adjust their techniques accordingly. The cinematography went for more photorealistic and cinematic visuals, using more wide-angle lenses than the original Lego Movie.

Batman has always inhabited a world of shadows and darkness, so the lighting takes this into account and contrasts it with over-saturated colors at places like Wayne Manor. Remember how Lego Movie used bricks to depict environmental effects like water and smoke? Lego Batman forgoes that for realistic rain, mist, and fog. It's believed that this makes Batman's world feel more dramatic and atmospheric — like a real film set.

8. The filmmakers have the ultimate sandbox

Rosario Dawson as Batgirl in The Lego Batman Movie

Think you have a big collection of Legos? No matter how many you've pulled together over the years, it can't compare to what Lego filmmakers have at their disposal. That's because everything in these movies is one hundred percent digital.

They have an exhaustive digital library of every type of Lego brick (internally referred to as "Lego elements") there is. Even the most obscure pieces are accounted for, from huge plates and gears down to tiny hair pieces and handguns. If every variety of Lego element was counted up, it would reach a total well into the thousands. And filmmakers have an infinite number of virtual bricks. Adding to the realism, every brick in the film has randomly added nicks and scratches to simulate real-world wear and tear.

Hardcore Lego enthusiasts noticed right away that The Lego Movie utilized elements that had never been seen before, such as President Business' rectangular hair. Lego Batman also introduces a number of new elements, but the filmmakers can't create with impunity. They're required to get permission from The Lego Group for every new piece they wish to make.

7. It has the biggest Lego sets ever built

The Batcave in The Lego Batman Movie

Director Chris McKay wanted the movie's sets to be ridiculously vast to reflect Batman's enormous ego. So you'll see the biggest Batcave ever in The Lego Batman Movie, a sprawling interior that houses an insane fleet of every kind of Bat-vehicle you could imagine.

The biggest challenge facing the animators was Gotham City. The filmmakers felt that it was such an iconic, recognizable location — even though it's been presented many different ways — that only a gargantuan set would do it justice. Gotham has a nearly infinite number of buildings, streets, back alleys, hideouts, facilities, and so forth, with incredible complexity and detail.

You might be wondering how big it could possibly be. If built out of real Lego bricks in the real world at Minifigure scale, the Batcave would measure a half mile from end to end (about .8 kilometers).

Think that's jaw-dropping? Gotham City would take up six and a half football fields.

6. Everything had to work like real Legos

Structural elements in The Lego Batman Movie

The Lego Batman Movie may be computer-generated, but it doesn't fudge the physics. Remember how the filmmakers have the freedom to create new Lego elements, with The Lego Group's approval (see: #8)? That doesn't mean they can create pieces that can't exist in the real world. It all has to move and function just like the real thing.

For example, did you know that some Lego bricks are more durable than others? The filmmakers didn't, but the builders at Lego HQ in Denmark explained that some pieces are made of sturdier plastic than others, for structural needs. In other words, some pieces have to be stronger to help hold up or hold together bigger or more complex models. Upon learning this, Lego Batman's crew incorporated those physics into the movie.

Another physical attribute that Lego takes very seriously is "clutch power." This refers to the stickability of the plastic studs and tubes that hold Lego bricks together. (Lego City fans may recognize that its main character is named "Clutch Powers." Cheeky.) Even though it's unlikely anyone will ever notice, clutch power was factored into all new pieces to ensure absolute authenticity.

5. Minifigures aren't contortionists

Minifigure movement in The Lego Batman Movie

By now, you've probably noticed how the Lego franchise always strives to be as true to the Lego brand as possible. It applies to every aspect of production, because the idea is always to produce locations, vehicles, and characters that look like they were built in the real world with real Legos. Just because it's taken to extremes that no one could ever build in the real world doesn't mean it shouldn't look, feel, and function as if it came out of the imagination of every child (and adult) who's ever played with Legos.

Another aspect that had to remain realistic is the way that the Minifigure characters move in the film. The Lego Group insists that these films not cheat by allowing Minifigures to stretch, bend, or contort in ways that real Minifigs can't. Want a character to hold up a single finger to point? Never gonna happen. Minifigs have tiny clawed hands, which means no fingers. Ever.

The characters' postures and movements were intentionally limited to the ways that real Minifigures work. But as is often the case, these confines sparked some seriously creative solutions. You may not even notice what the characters can't do, because you're too busy being astounded by everything they can.

4. Even facial expressions were rendered the Lego way

Facial expressions in The Lego Batman Movie

With Lego films completely beholden to The Lego Group's own rules and principles, you'd be tempted to think that somewhere in there — the characters' emotions, for example — the filmmakers might be given a little leeway.

Nope. On real Lego Minifigures, decals are overlaid onto those teeny little faces to give them facial expressions. Look close enough, and sometimes you can even see transparent outlines around the eyes or mouth. To maintain accuracy, the characters in the films appear to use the same kind of decals — even though they're constantly in motion.

To accomplish this effect, the expressions of CGI Minifigs are rendered with those same transparent outlines. Gradually, a black line of a smile might become a frown, through the magic of animation. This is nothing new. But Lego films take the time to add in the tiny decal details in every frame to help sell the idea that these are real Minifigures that have come to life.

3. Joker's evil pals include some surprise guests

Joker and Harley Quinn lead the Rogues Gallery in The Lego Batman Movie

An early sequence of the film finds Joker assembling Batman's entire "rogues gallery" of enemies for a full, all-out assault on Gotham. Which Batman has to stop, of course.

This huge group of baddies includes virtually every baddie Batman has ever gone up against, including more obscure villains like Kite Man and King Tut. It's a huge, impressive group, but Joker doesn't stop there. Reaching out beyond Gotham, he drafts what he calls "the worst villains in the history of the universe."

Who are these ultimate baddies? We can't speak for all of them; we imagine there are several in the background who don't get lines. But the movie's credits identify supervillains called "The Ubers," listing Lord of the Rings' Sauron, King Kong, and Harry Potter's Voldemort as the members that speak in the film. Giving away who voices them would be a little too spoilery (you can find them elsewhere if you just have to know), but we'll tell you this about that last evildoer we mentioned...

2. Ralph Fiennes does not voice Voldemort

Ralph Fiennes as Alfred in The Lego Batman Movie

Imagine it. Not only do you have permission to use one of the greatest fictional villains of all time in your movie, but you've already secured the actor who played that very mega-villain 5 times on the big screen as a member of your cast. So getting him to reprise one of his most famous parts would be a no-brainer, right?

Wrong.

Celebrated, award-winning actor Ralph Fiennes portrays Alfred in The Lego Batman Movie. Alfred Pennyworth, as all good Bat-fans know, is Bruce Wayne's faithful butler and surrogate father figure. Voldemort's part in Lego Batman is not a very big one, but it seems like a pretty obvious move to ask Mr. Fiennes to lend his voice to a second character. It's not unfeasible; Fiennes' Alfred and Voldemort sound nothing alike.

But the filmmakers didn't do it. Or maybe he said no. We don't really know what happened. But Voldemort is voiced in the movie by another actor. (Don't ask, we're still not telling.)

1. Lego Batman finally asks a 76-year-old question

Robin's colorful costume in The Lego Batman Movie

Batman is a dark knight. A detective who works in the shadows. A mature hero who deals with very grown-up crimes. So what's he doing running around with a kid dressed in a bright, technicolor costume?

Come on, you know you've wondered. Everyone has. The whole concept of Robin is somewhat antithetical to who and what Batman is — not just his "lone wolf" way of working, but the very tone of his entire world. If you take away how "Batman and Robin" always go together in our imaginations, Robin's very existence in Batman's world makes little to no sense. Yet it's rare that anyone in the comics questions this obvious conflict of ideologies.

The Lego Batman Movie dares to ponder it. Not only have they given Robin a reason for being, they even went to the trouble of constructing a backstory for that oh-so-colorful costume he wears. Other interpretations have attempted to justify Robin and his goofy outfit (Batman Forever comes to mind...unfortunately), but Lego Batman is the first time the question has been asked and answered satisfactorily. The Dynamic Duo has never been such a joy to watch.

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Do you know of any other fun facts surrounding the Lego Batman's first solo adventure on the big screen? Let us know in the comments.

The Lego Batman Movie is in theaters now.