A Supergirl movie to follow-up Man of Steel in the Sasha Calle was cast as Kara Zor-El herself. The DCEU version of Supergirl will appear first in next year's The Flash movie alongside Ezra Miller's Barry Allen and Ben Affleck's Batman/Bruce Wayne.
With the Girl of Steel herself cast, it's only a matter of time before Warner Bros greenlights a full Supergirl movie, if it hasn't already. Fortunately for any potential director, there have been many excellent Supergirl stories over the years that could be adapted into a thrilling movie.
The Furies Of Granny Goodness (Batman/Superman: Supergirl)
Following the epic "Crisis On Infinite Earths" event in which Supergirl died, Superman's cousin didn't feature in the comics for a long time. That all changed with Jeph Loeb's Batman/Superman story "The Supergirl From Krypton," which was later adapted into an animated movie.
In it, Supergirl arrives and Zack Snyder's Justice League, and the story also features Kara being trained on Themyscira too.
Reign And The Worldkillers (New 52/CW Supergirl)
For its first two seasons, the Supergirl TV series starring Melissa Benoist was criticized for relying on Superman villains and characters such as Mon-El and Toyman rather than any of Supergirl's own enemies, so for season three, the showrunners focused on the Kryptonian "Worldkiller" called Reign.
In the comics, Reign and her fellow Worldkillers were created as genetic weapons by Kryptonian scientists, whereas their TV incarnations were made through dark magics by the Kryptonian sorceress Selena - the villain in the original 1984 Supergirl movie. Bringing in Reign would make for some epic encounters in a new Supergirl movie, and the possible return of Selena would be a neat twist for fans.
Galatea And The Cus Project (Justice League Unlimited)
While Supergirl would be introduced in Superman: The Animated Series, Justice League Unlimited that she was truly allowed to shine. One of the animated Supergirl's best stories revolved around the Cus Project, a secret government organization lead by Amanda Waller that was designed to counter the Justice League, and the clone they created of Kara called Galatea.
While Galatea looked a lot like the comics' Power Girl, she was actually a psychopathic government-controlled villain. Having the US government directly work against Supergirl would be an interesting place for the Supergirl movie to go, and having Kara and Galatea fight would be incredible.
The New Cyborg Superman (New 52/Rebirth)
One of the biggest changes the New 52 comics reboot made involved the villain known as the Cyborg Superman. Previously his human identity was Hank Henshaw, a name Supergirl TV fans will recognize as the one Martian Manhunter co-opted. The New 52 changed things so Cyborg Superman was actually Supergirl's father Zor-El, who was transformed into the slave of Brainiac.
Supergirl's defense of her altered father, even after his attempted invasion of Earth, damages the public's trust in her, something she's still trying to regain in the Rebirth stories today. All of this would make a fantastic and action-packed plot for a movie.
New Krypton And Superwoman (Who Is Superwoman?)
In 2009, the bottle city of Kandor, the last city of Krypton shrunk by Brainiac before its destruction, was finally restored to its correct size on a planet dubbed "New Krypton." Supergirl was a crucial element of the New Krypton saga, as her parents were the ones who became the planet's leaders.
Tensions between Earth and New Kandor reach critical levels when Kara's father Zor-El is killed by an Earth assassin, and Supergirl is further challenged by the mysterious Superwoman who doesn't seem to be on her side. While the saga might be too much for a single movie, if Warner Bros is planning a trilogy it could be perfect.
Rogol Zaar And Mr. Oz (DC Rebirth)
The recent DC Rebirth era of Superman and Supergirl comics has been dominated by two interconnected storylines related to two characters: alien mercenary Rogol Zaar and the mysterious "Mr. Oz." Rogol Zaar would be the main one for Supergirl since he claims that he was the one that destroyed Krypton and is currently hunting down all surviving Kryptonians, something she doesn't take kindly to.
However, Mr. Oz may be of interest too, since he was eventually revealed as an aging and bitter Jor-El, who would go on to kill Kara's "Cyborg Superman" father as a supposed "mercy killing."
Brainiac Attacks (Injustice 2/Superman Unbound)
With Darkseid now a part of Zack Snyder's Justice League, probably the biggest remaining villain in the DC universe not to appear in the movies (outside of a Crisis-level enemy such as the Anti-Monitor or Perpetua) is the destroyer of worlds, Brainiac.
Brainiac is a villain fans have wanted to see on the big screen for a long time and he works really well with Supergirl, as seen in either the Superman Unbound animated movie or the video game Injustice 2. In both, Kara is traumatized by witnessing the abduction of Kandor city by Brainiac but has to fight through her fear when he tries to do to Earth what he did to Krypton.
The Red Lantern (New 52)
The New 52 series of comics put Supergirl in a very bad place. The loss of her home planet, learning that her father was corrupted by Brainiac, and her best friend getting turned into the villain Silver Banshee left Kara filled with repressed rage. It was perhaps no surprise that she would get recruited for the Red Lantern Corps.
What followed would be an excellent way to introduce the Lanterns of Rage into the DCEU (assuming the Green Lantern HBO show is set in the movie universe) as Kara learns to deal with her anger while being more powerful than Superman.
Bizarro Girl (Post-Infinite Crisis/Supergirl TV)
Following on from Supergirl's return and the destruction of New Krypton, Kara received her own version of Bizarro - the distorted mirror copy of Superman with inverted powers and not much intelligence. "Bizarro-Girl" is one of the most entertaining Supergirl comics, especially as it brings in the twisted Bizarro World.
The Supergirl TV series's first season also brought in Bizarro-Girl but with a more serious plot that would probably work better for a movie, which sees slimy businessman Maxwell Lord twist the DNA of a normal human girl into a broken copy of Supergirl.
Origin Of The Kryptonian Scout Ship (Man Of Steel Prequel Comic)
The biggest question about Supergirl's entrance into the DCEU is how exactly she's going to arrive. This question may actually have already been answered, along with clearing up the mystery of that open cryo-pod on the Kryptonian Scout Ship - which made a return appearance in Zack Snyder's Justice League. In 2013, Zack Snyder, Geoff Johns, and David Goyer wrote a Man of Steel prequel comic that reimagined Kara Zor-El as an ancestor of Superman's rather than his cousin.
She was actually the captain of the Scout Ship seen in the movies, and the open pod was hers. According to the end of the comic, she survived the crash on Earth and may still be alive. It's unlikely that the Supergirl movie will follow this proposed origin, but it'd clear up some of the lingering mysteries from the Snyderverse.
