The Arrowverse has continued to add vital characters to the small screen, some of which may have never made it from the page of DC's comics. Many of these television heroes and villains might actually be a better fit for cinema though and are being underutilized on the CW.
Whether it's based on their power set, the importance of the character themselves, the costuming, or the stories they have been involved with, these Arrowverse characters are absolutely set to thrive on the big screen if they ever get the opportunity. Some of these vigilantes and antagonists will be getting a chance in the DCEU in the near future with the forthcoming The Flash and Black Atom films.
Reverse-Flash
One of the unpopular opinions surrounding the Reverse-Flash in the Arrowverse is that the character has actually been underused. Although Thawne has reappeared time and time again, his true power has yet to be unleashed because it would majorly rewrite Barry Allen's future.
The character's abilities are also a little suppressed on a budget, but a cinematic version with a clear villainous arc and the room to make risky narrative decisions in regards to the destruction he can cause would be incredible to watch. The DCEU might be the place a worthy Reverse-Flash is put onscreen with an updated costume as well.
Supergirl
Supergirl has had her own show within the Arrowverse for some time but as it comes to an end, she's about to make her debut in the DCEU in The Flash film with Ezra Miller. Because of the nature of an ongoing series, with a limited budget, Supergirl's powers were de-escalated despite many iconic moments.
In many versions across comic books, animated shows, and even films, she is stronger than Superman, but her abilities were limited throughout the series. With the Multiverse at stake and the Flash by her side, the big-screen iteration should be able to go all out in using her powers especially in comparison to other characters who will not have plot armor to protect them as a Big Bad. Often Kara would be weaker in order for the villain-of-the-week to have a better chance against her.
Atom
The Atom, whether it's Ryan Choi or the more prominent Ray Palmer, never quite lived up to his superhero potential. Budget is again a big issue here, alongside the fact that the hero couldn't be too overpowered or else the narrative stakes would be too low to engage the average viewer on a weekly basis.
Atom can shrink and grow to incredible sizes but the character rarely got to use the power on screen. When used in future DCEU movies, the powers of the Atom can be revealed with great complexity. The CGI alone is sure to create larger improvements to the quality of the design as well as Atom's shrinking abilities, which are comparable to his Marvel counterpart, Ant-Man.
Captain Cold
Captain Cold was written out of the Arrowverse before the character could complete his arc. Although he was largely redeemed, it was interesting to see this heroic side of the character. What's more, his weapon was really a one-hit-wonder.
Captain Cold has a vast amount of icy gadgets throughout the comics but the Arrowverse only portrayed him with a single cold gun. In regards to both his personality and the range of weapons on offer, the big screen might be able to capitalize on the potential of the cool Flash villain.
Vixen
Although Vixen's ancestor has been used throughout the Arrowverse, the current incarnation of the hero has been sparingly featured on the screen outside of her animated show. This is in large part due to the complicated nature of her abilities.
Her powers allow the character to take on the skills of a creature from the animal kingdom, thanks to her totem. It could be very cinematic but its limited use has meant that the surface hasn't even been scratched in regards to what could be achieved here. At the very least, larger spirit constructs focused upon the animals would look incredible from a movie studio.
Gorilla Grodd
Gorilla Grodd is a character that won't ever look perfect unless given the proper time to develop. Budget is one aspect of this, but what's more, is that a weekly TV show's CGI isn't given the full amount of time it needs when it is in the post-production stage, which often rushed to meet a weekly deadline.
That means that the story being told with the character is going to have to be limited. It has to be said that the Gorilla Grodd seen in the Arrowverse is far better than expected. That technology can be taken to another level though with the resources of a larger studio. Grodd could be the big bad he was intended to be.
Killer Frost
Killer Frost was once a villain in the Arrowverse but had made the transition to hero as so many other antagonists have done before her. This really limited the character as 'killer' was in the name. Frost has also had a more heroic turn in the source material, but the arc was far greater.
Killer Frost deserves her own solo film which deals with the complexities of this redemption. The movie could flesh out and explore her transformation from a villain to a reluctant hero who rediscovers her own humanity. Much like Captain Cold, her abilities could be made a lot more impressive in a cinematic format as well.
Mr. Terrific
Mr. Terrfic's story was certainly intriguing throughout his time in the Arrowverse. The comics have now seen the inventor lead his own team though, with his gadgets expanding and his importance increasing. On TV, he was underutilized among a large ensemble of established characters who were often prioritized over him in both screen time and narrative importance.
With a better budget that can be focused further on the character, Mr. Terrific would thrive. Besides a wider range of technology available, a cinematic version of the character could allow for the creation of the Terrifics, a cult sci-fi superhero team that is in dire need of an adaptation.
Ragman
Ragman's design and power set became far too complicated for a TV show. He was overpowered which meant he could solve any crisis rather easily, and the suit itself was very difficult to animate when his abilities came into full force. The character was therefore written out of Arrow.
Ragman wasn't given a proper chance on screen and it just didn't work within a TV format. A film would certainly match the character better as a bigger budget could properly portray his unique power set. Within a limited story, the stakes can be made a lot higher, which means Ragman can be unlocked to his full capacity.
Livewire
Livewire was a character with a big powerset that couldn't really thrive within the confined setting of the Arrowverse. The character was given her own redemptive arc, but this stopped her from being unleashed as the big bad she ought to have been.
On the big screen, Livewire might actually be utilized as a proper villain. Her powers are already visually striking which would help with a more cinematic portrayal, plus with a Supergirl that has every ability unlocked, Livewire can step it up another gear.