NYCC: Maxwell Atoms talks blending Batman with Mystery Inc. for Happy Halloween, Scooby-Doo!

When he was tapped to write, direct, and produce Happy Halloween, Scooby-Doo!, Maxwell Atoms decided to go for broke with the film's guest stars. The movie — whose first trailer SYFY WIRE exclusively revealed over the summer — features not only Elvira (Cassandra Peterson) and Bill Nye (voicing himself), but also a villain from the Batman universe: Dr. Jonathan Crane, aka Scarecrow (Dwight Schultz). Appearing at this year's New York Comic Con, Atoms admitted that he wasn't sure Warner Bros. would let him get away with merging all these characters and IPs together.

"I was sort of shocked that I got away with that," he said. "I feel like every time I work for a different studio, they're always like, 'Yeah, we want synergy.' And then you're like, 'What if we did this and this?' And they're like, 'No ... just no.'"

The director also revealed that the decision to utilize evil pumpkins in the film was a natural extension of the 2003 Halloween special for The Grim Adventures of Billy & Mandy, which he created for Cartoon Network.

"I just wanted to lean on the Halloween stuff and make it the Halloween-iest Halloween special I could," he explained. "When I started writing it, I realized that pretty much any monster is a Halloween monster and also a Scooby-Doo! monster. I think that's how I ended up with pumpkins as one of the villains, because I had pumpkins in a Halloween special for Billy and Mandy about 20 years ago, and this was sort of convergent evolution where I decided, 'Well, there's nothing more Halloween-y than pumpkins.'"

Watch the full panel below:

Bill Nye factors into the story with Mystery Machine X, a technologically advanced and Knight Rider-esque van that puts the gang's usual vehicle to shame. Fred (voiced by Frank Welker) isn't such a fan, though, claiming that the MMX has no soul.

"I don't know if I'm on Bill Nye's side on this one," Atoms said. "I'm sort of a Fred man, but it doesn't hurt to have laser guns in your hubcaps." When it came to incorporating the famous Science Guy and Peterson's Mistress of Darkness into the narrative, the director stated that he's "kept up with both of them over the years. I did go back and watch the old Elvira movies and a bunch of the TV shows that I could find on YouTube. I watched a bunch of Bill Nye [and] that's about it. That and imagination, I suppose."

Matthew Lillard ("Shaggy"), Grey Griffin ("Daphne"), and Kate Micucci ("Velma") round out the rest of the central voice cast. Welker pulls double duty as the voice of Fred and Scooby. "Our job, collectively, is to make sure that this brand, that this cartoon, that these characters go on to the next generation. So that in 100 years from now, the storytelling is still relevant for kids then," Lillard said.

Happy Halloween, Scooby-Doo! is now available to own or rent on home video. You can check out the movie's first eight minutes at the end of the NYCC panel (starting at 35:33).

Click here for SYFY WIRE's full coverage of New York Comic Con 2020.