The secrets of "Marvel's Agents of S.H.I.E.L.D." Season 4 just got a lot less classified.

During their whirlwind tour of Comic-Con International, the key creative personnel made public some of the new elements of ABC's Marvel series' upcoming season -- including the addition of a fresh incarnation of the classic superhero/horror character Ghost Rider and greater access to the stable of established Inhuman characters -- and zeroed in on some of the finer details after their panel.

After a third season that severely tested its characters' resolve in the extreme -- to the point that by the season-ending time jump Daisy Johnson (Chloe Bennet) had left S.H.I.E.L.D. to pursue her own agenda and Phil Coulson (Clark Gregg) stepped away from his duties as Director to return to the field -- things are about to get even darker, and more than a little mystical.

Enter Ghost Rider"The show's gotten darker as you put the characters through their paces," said executive producer Jed Whedon. "I think that's just a natural thing that happens really with any show ... People have to go through a journey, so you end up putting everybody through pain. Now, pretty much everybody's had some gnarly experience, so they're all more weathered and seasoned. So I think it's only natural for the show to take on a darker tone."

"The fact that we have Ghost Rider now going to be on the show, that in and of itself comes with some pretty hardcore violence and grittiness -- and cars on fire," added executive producer Maurissa Tancharoen.

The Ghost Rider in question is not the traditional comic book character Johnny Blaze, the demonically possessed, flaming skulled stunt motorcyclist played by Nicolas Cage in the 2007 Sony film that predated the Marvel Cinematic Universe. The new version is derived from a more recent 2014 reworking from Marvel's comic-book division: Robbie Reyes is an East L.A. teen with a taste for high-octane muscle cars who, after being gunned down in a gang-related shooting is inhabited by a similarly skull-blazing entity which happened to be his deceased uncle, a Satan-worshipping serial killer.

The introduction of Ghost Rider comes just as Marvel's feature film side is about to open the door to the MCU's magical side with the fall release of "Doctor Strange." "It's one of the reasons we feel like Ghost Rider will fit this year," says Whedon. "The Cinematic Universe is sort of being opened up into that world. But the Marvel approach is that magic is science that we don't yet understand. So we're going to have both the introduction of magical elements on our show, as well as very hardcore science ... I don't really want to explain magic. So 'Doctor Strange' will do it."

Tripping on LMDIn terms of that hardcore science, the concept of Life Model Decoys -- lookalike artificial intelligence stand-ins for S.H.I.E.L.D. agents -- has been part and parcel of the S.H.I.E.L.D. comic books since the 1960s and occasionally obliquely name-checked on the show. The concept will finally be explored in the fourth season, says Whedon, "not necessarily a threat -- though, down the road, any new technology maybe won't go great. For us right away, it represents their desire to control things in a way. They don't like what happened last year. They don't want that to happen. The whole concept of the decoy is that someone else could be sent in to do that job. So it comes from an altruistic notion, initially."

The team's new resident, kind-of-mad scientist Holden Radcliffe (John Hannah) will lead the LMD charge, said Whedon, largely out of his "desire to prove that he's a good guy, and the things that happened were beyond his control. And yes, he has a scientific mind, but his heart's in the right place."

"[But] we know that in the Marvel Universe, the exploration into A.I. has had some dire consequences, in 'Age of Ultron,'" added Tancheroen.

His First Name Is 'Agent'Coulson's self-demotion from the leadership seat he inherited from Nick Fury back to foot soldier makes perfect sense to Gregg after the series of life-and-death big picture calls he's been required to make. "I'm not surprised he's not the Director anymore," says the actor. "Once again, he's a guy who's first name is 'Agent,' and I think there's a comfort factor there. He didn't like being on Zephyr One calling in the different units."

"We've had Coulson on this journey, as a director -- it's harder to be the Director," says executive producer Jeff Bell. "You're sending people into battle. Lives are being lost. You lose a hand. Suddenly, you're losing some of your own humanity. How dark do you go? Coming back out of that, it felt like he had done that."

"And, honestly, we love Coulson from 'Iron Man,'" added Bell. "We love the guy who goes out to talk his way out of anything. We like him boots on the ground going into situations. And as director sometimes, there was conflict with doing that. So to find him, been there done that, sort of world-weary at that, and then suddenly not ... is something Season 4 will look at."

"How does he feel about the new director?" muses Gregg about the mystery character that will be running S.H.I.E.L.D. in Coulson's wake. "A little bit hard to tell so far. I don't know. We don't know too much about the new director yet. All I can tell is that it seems like S.H.I.E.L.D. is no longer an outlaw organization. It has now fallen under control of some governments in line with the Sokovia Accords, and those 'powers that be' have chosen somebody else they're comfortable with. It remains to be seen if any of us from the S.H.I.E.L.D. team will be as comfortable with them. The rumors I'm hearing are exciting. It's an interesting idea that they've got about where that might go."

"Because the world around them has changed, S.H.I.E.L.D. has had to change," explained Bell. "The Sokovia Accords and what happened in the last 'Captain America' movie will also trickle into how our world is. So with the rise of the Inhumans, our characters had to engage that, although we were very secret. So that will continue to evolve as we go forward this season."

Bring on the Giant Teleporting DogMarvel Studios cancelling its plan for a big-screen "Inhumans" film suggests that the race of super-powered characters had proven a better fit for "Agents of S.H.I.E.L.D.," where one leading character, Daisy, was ultimately revealed to have Inhuman ancestry. The door now looks significantly more open for some of the classic Stan Lee / Jack Kirby-created comic book Inhumans, including royal family members like Black Bolt, Medusa, Karnak, Gorgon, Triton, and Crystal. "We like [the Inhumans] in our world," said Bell. "So you'll see more of that this season."

"We do have a little more freedom," revealed Whedon. "We've told a couple seasons of stories, but now we do have some more freedom. So when we return to focusing on Inhumans, we'll be able to do a little bit more ... Right now, that's not our focus, but it's out there.

"You want the dog, right?" laughed Bell, referencing the enormous Inhuman canine Lockjaw, who can teleport himself at will. "To be discovered," he grinned.

"Agents of S.H.I.E.L.D." Season 4 premieres September 20th at 10 p.m. on ABC.