Spoilers for The LEGO Batman Movie follow in the post below. If you haven’t seen the ending of the movie, turn back now. 

Fans of The LEGO Movie may have been surprised to learn that while The LEGO Batman Movie is indeed a Batman movie, it’s also still very much a LEGO movie and indeed pulled off another third act surprise just as The LEGO Movie did. One might think that having almost every Batman villain ever in The LEGO Batman Movie would have been enough (for more on this, check out Dave’s extensive Easter Egg roundup), but no—the team behind The LEGO Batman Movie decided to bring in villains from all kinds of properties. Sauron from Lord of the Rings, Voldemort from Harry Potter, and even King Kong all play major roles in the third act of The LEGO Batman Movie, as Joker unleashes all the baddies from the Phantom Zone to terrorize Gotham City.

So how did this idea come about, and why include villains like King Kong in a Batman movie? Well, speaking with EW, director Chris McKay cites his desire to “cross the streams” as dating back to Last Action Hero:

“The Joker needed to up his game and prove himself, and we talked about this being the Joker’s big romantic grand gesture. So in order to do that… I loved the [1978 Richard Donner-directed] Superman and the idea that the Phantom Zone, in our world, could possibly house all of the villains from other LEGO universes. It’s almost like Cabin in the Woods. Or, in Last Action Hero, when Charles Dance says, I can go into all these movies and I can bring out Jack the Ripper or King Kong. When I was younger, watching that movie, I was somehow expecting a scene between King Kong and Arnold Schwarzenegger, and I was always bummed it didn’t go there. [Laughs.] But in our world, we can do something like that and unleash all these characters into Batman’s world.”

Believe it or not, there were plans for even more villains to appear—ones that would’ve cinephiles very happy—but they were abandoned in favor of keeping the film’s references mostly kid-appropriate:

"I would have had Kathy Bates from Misery, and [Sherlock Holmes nemesis] Moriarty, and at one point I pitched Daniel Day-Lewis’s character from Gangs of New York and David Carradine from Kill Bill. At a certain point, though, you have to weigh what characters the kids going to get. In LEGO, it’s sometimes hard to get a really quick interpretation of something. I was already worried that we weren’t doing enough with some characters. Also, at one point, we did put HAL from [2001: A Space Odyssey] into the movie, but it was a tough read. Maybe in future movies, we’ll try to bring more characters in."

Just saying, if Bill the Butcher had been in The LEGO Batman Movie it may have qualified for best film cameo ever. But the ones McKay and his team settled on worked well, and he reveals that he did indeed have to get J.K. Rowling’s permission to use Voldemort, and she even suggested specific spells for him to use. But one odd choice the team made was to have Ralph Fiennes not voice Voldemort, even though he was already part of the film as Alfred. McKay explains why:

“At one point I approached the studio and asked if I could get Ralph to do both parts. But unless you’re going to do a scene where Alfred and Voldemort confront each other, I didn’t want something to feel like a missed opportunity. [Laughs.] I do remember when I was pitching him the movie, I said, ‘Yeah, then all of these bad guys are going to be unleashed like King Kong and Sauron and Voldemort—‘ And then I stopped for a second because I realized who I was talking to.”

That one still feels like a weird choice—it’s more distracting to have Fiennes not voicing the Dark Lord. But while some fans were dismayed that the third act involved non-Batman villains, it makes sense when you think of the film as part of the LEGO Cinematic Universe. The first LEGO Movie revealed that all of this action is taking place as part of the imagination of a young kid, and kids with toys are definitely going to cross-pollinate their Batman battles with whatever other villain toys are at their disposal.

McKay talked a bit about this LEGO Cinematic Universe, revealing that we’ll learn more about the world in the upcoming LEGO Ninjago Movie and The LEGO Movie Sequel.

“Everyone says this, but for lack of a better phrase, there’s a LEGO cinematic universe that we’re building that has a sci-fi premise, as far as the world that the movies are taking place in for the majority of the running time, and the other world that’s out there. I think over the course of the movies, we’re building out the relationship between those. There’s no mandate necessarily to do that, but we are very actively working to find all of the rules and develop that relationship between the real world and the LEGO world. You’ll start to see it in what we’re doing with Ninjago and what what we’re doing in LEGO 2.”

As for whether Batman is a part of the universe going forward, the answer is absolutely:

“There’s definitely a part for Batman in LEGO 2. Everyone loves Will Arnett and the Batman character. There are going to be the repercussions of what’s happened in [LEGO Batman]. If you agree that he went through some change, there’s more stuff in store for Batman in LEGO 2.”

Of course given the box office success, we should be hearing word about The LEGO Batman Movie Sequel any day now.