The The Dark Knight franchise was still going.
But once the Arrowverse was created in 2012, starting with DCEU was getting further fleshed out. Throughout the first few years of DC’s cinematic universe, The CW was forced to remove multiple characters that were about to appear in the films. Additionally, more characters were forbidden from showing up because of franchises. There were even instances when the Arrowverse producers had to change plans at the last minute after initially being granted certain characters.
Currently, the limitations have become more fluid with Tyler Hoechlin’s Superman set to get his own Arrowverse spinoff, Batwoman after The CW had been forbidden for years to reference Gotham City or any major Batman character. In big and small ways, the Arrowverse is incorporating more of the larger DC Universe as the seasons go on, but thus far, here are DC characters that Smallville and the Arrowverse have been prevented from using.
Wonder Woman
One of the most iconic heroines from DC, Diana Prince has never been able to The CW on any of the ongoing shows or on Smallville. While there was the prequel series Amazon that was in the works years ago, which would have followed Diana’s origin story at Themyscira, it never took off. After several attempts at developing the pilot, The CW scrapped Amazon altogether, and that was the network’s only attempt to bring Wonder Woman to the small screen. During Smallville’s run, the executive producers tried several times to get the approval from DC and Warner Bros. to bring Diana into their universe, but during the earlier seasons, Warner Bros. was actively developing a feature film, including the version by Joss Whedon, which is why they refused to let Smallville get access to Diana.
Smallville Season 11, the tie-in comic by Bryan Q. Miller, finally introduced Wonder Woman into that universe. However, Miller revealed in an interview with David E. Kelley’s Wonder Woman show for NBC was in the works. Kelley's series ultimately didn’t pan out, but the Smallville writers were able to sneak in a couple of allusions to Diana throughout the show’s run, with Easter eggs about Themyscira, Queen Hippolyta, and Chloe Sullivan having met a “wondrous woman who’s gonna throw you for a loop.”
In the Arrowverse’s case, Gal Gadot’s ongoing Supergirl, Lynda Carter did make special appearances on both series as part of their legacy casting.
Batman
Warner Bros. Studio has always held a tight grip on Gotham City’s Caped Crusader. Before Smallville was even an idea for Warner Bros. TV, they were developing a Despite never gaining access to Bruce, the series did make a few allusions to Gotham City as well as Chloe saying she met “a billionaire with high-tech toys.”
The Arrowverse, however, managed to break through the barrier more than Smallville, especially in the last few seasons. After several Batman foes had been introduced in the early years, Gotham City and Bruce were name-dropped in Arrow season 6, confirming that a version of the Dark Knight was on Earth-1. When Elseworlds, several of Batman’s foes were referenced, and the crossover itself was a smorgasbord of Batman-centric Easter eggs. Since the show premiered, Bruce has still been missing, which set up Kate to take up his mantle and become her own hero.
However, through exposition in the first season, more details have been revealed about this version of DC Comics’ iconic detective, including the fact that Warren Christie is Arrowverse’s Batman. Whether or not he will ever get to play the real Bruce or suit-up as the Dark Knight remains to be seen.
Vandal Savage
While the Arrowverse was able to introduce Vandal Savage as the first villain for an alias by Arrowverse’s Vandal as a tribute to Smallville.
The Flash
While DCEU’s version of Flash is getting his own movie in 2022, the previous attempted projects were the main reason why Smallville couldn’t go further with Impulse.
Aquaman
Before Jason Momoa's Aquaman, Smallville was able to use Arthur Curry throughout the later seasons as a recurring Justice League member. The creators even attempted at launching a spinoff, with Justin Hartley (who would go on to play Smallville's Green Arrow) cast as the iconic hero in a pilot that didn't go to series. In the Arrowverse, the King of Atlantis has yet to appear, and Momoa's ongoing Atlantis having been established to exist in Earth-Prime, post-Crisis, Arthur's existence hasn't been established thus far.
Ted Kord
Smallville was able to play with the Blue Beetle mythology in one of their final episodes of the 10th season with both Jaime Reyes and Ted Kord showing up. In the Arrowverse, however, it has been a battle to bring Ted into their shared universe as Kord Industries as well as the CEO himself have been name-dropped multiple times over the years. At one point, Arrow was set to finally introduce him with Brandon Routh playing Ted, but plans for Ted becoming Blue Beetle were never solidified. However, Warner Bros. came in during the 11th hour and told the producers that they had other plans for Ted, and Routh played Ray Palmer a.k.a. The Atom instead. Despite that, Ted has yet to appear in any other DC live-action projects, neither the big nor small screens.
Deathstroke
Even though Slade Wilson has appeared in the Arrowverse with Manu Bennett playing him in the first two seasons of Arrow, the DCEU ended up blocking the showrunners from using him in the later seasons. Despite a brief return in the third season, fans wouldn't see Guggenheim had confirmed that their Deathstroke had been benched because of the DCEU after his final Arrow appearance in November 2017.
The Question
Another iconic hero that viewers and even Arrowverse producers have been wanting to see is Vic Sage a.k.a. the Question. With shows like Arrow and Batwoman being the grittier shows of the franchise, someone like Sage would have been a perfect fit. However, the Question was another hero that was hands-off for The CW because of Warner Bros. having different plans for the Hub City-based hero. While his city has been established as existing in the franchise, Guggenheim revealed in 2017 that they had tried to introduce the Question, but were ultimately not given the green light. Despite being denied access to him, the Question has still not appeared anywhere in the DCEU.
Oracle & Birds of Prey
Prior to the Arrowverse introducing the Batman mythology through Batwoman, another major Batman family member was forbidden from appearing on the shows or even mentioning her code-name to Felicity Smoak: Barbara Gordon, or more specifically, Oracle. In the fourth season, Felicity was officially given the code-name Overwatch as Oliver references that he was going to go with Oracle, but that it was taken. The name even popped up as Bird of Prey-inspired episode in the seventh season.
Suicide Squad
One of the earliest concepts that Arrow introduced from the DC Universe was the Suicide Squad, which was a large plot point in the second season. such as Deadshot, Bronze Tiger, and Shrapnel were part of the first team led by Amanda Waller, which became one of viewers' favorite storylines. Ghost Initiative in later seasons, the Suicide Squad that viewers had come to love was forever dead because of the cinematic counterpart.
Green Lantern
Bringing the Green Lantern Corps into the Arrowverse has been one of the franchise's biggest challenges as Warner Bros. has consistently denied their proposals. Out of all the heroes that they have referenced, the Emerald Knight has been teased the most throughout the years. Including the multiple mentions of Ferris Air, Oliver visiting Coast City, and even a faceless cameo of Hal Jordan, the allusions to the Green Lantern mythology have increased in later seasons. The Elseworlds crossover set up the idea of John Diggle being a Green Lantern in another universe, hence the big tease in the series finale when he discovered an alien box with glowing green energy inside of it. Even though the ring is never seen, it is heavily implied that Diggle found a Lantern ring, setting up his next adventure in the Arrowverse.
But that's still up in the air according to Arrowverse's new Multiverse, Warner Bros. keeps a tight grip on the Emerald Knights.
In the previous seasons, the studio was actively trying to reboot the Green Lantern franchise after the 2011 film was a financial and critical failure. As the DCEU was being set up, Green Lantern Corps was one of the original movies that they announced, but it has been in development since 2014. That was the main reason why Arrow or any of the other shows couldn't fully explore the mythology or have a Lantern show up. But with the HBO Max series, at least one of the other Arrowverse Earths will finally get access to Green Lantern unless Diggle returns in any of the other shows in future seasons as an Emerald Knight.