spoilers season3 episode23Title: Battles Lost and Won

Directed By: Jesse Warn

Air Date: June 18th, 2018

Written By: Robert Rovner & Jessica Queller

Official Description: SHOCKING SEASON FINALE – Supergirl (Melissa Benoist) and team take on Selena in an epic battle for Earth.

Reoccurring Cast:

Guest Stars: Patricia Aria (Betty Buckley)

Special Notes: 

spoilers season3 episode22Title: Make It Reign

Directed By: Armen V. Kevorkian

Air Date: June 11th, 2018

Written By: Ray Utarnachitt & Cindy Lichtman

Official Description: SUPERGIRL PREPARES FOR BATTLE – Supergirl (Melissa Benoist) learns the true depth of Serena’s (guest star Anjali Jay) nefarious plans for Earth. Supergirl, Mon-El (Chris Wood) and Alura (guest star Erica Durance) must devise a plan to stop her before Serena gets to Earth. J’onn (David Harewood) prepares to say goodbye to his father (guest star Carl Lumby).

Reoccurring Cast:

Guest Stars: M'yrnn J'onzz (Carl Lumby) | Serena (Anjali Jay) | Alura (Erica Durance)

Special Notes: 

spoilers season3 episode21Title: Not Kansas

Directed By: Dermott Downs

Air Date: June 4th, 2018

Written By: Gabriel Llanas & Anna Musky-Goldwyn

Official Description: KARA CONSIDERS A MAJOR LIFE CHANGE – Kara makes a major life decision. Meanwhile, J’onn finds out that special DEO-caliber guns have hit the streets of National City.

Reoccurring Cast:

Guest Stars: 

Special Notes: 

spoilers season3 episode20Title: The Dark Side of the Moon

Directed By: Hanelle Culpepper

Air Date: May 28th, 2018

Written By: Derek Simon & Katie Rose Rogers

Official Description: SUPERGIRL LEARNS A STUNNING SECRET ABOUT KRYPTON – Supergirl is stunned to discover that a part of Krypton survived. Meanwhile, Alex is attacked while out with Ruby, and Lena considers how far she will go to keep Reign contained.

Reoccurring Cast: Ruby (Emma Tremblay)

Guest Stars:

Special Notes: Rumors have it that J'onn is actually taking the form of Alex this episode. While Alex is truly wearing the odd new armor, the regular Alex is actually J'onn.

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spoilers season3 episode19Title: The Fanatical

Directed By: Mairzee Almas

Air Date: May 21st, 2018

Written By: Paula Yoo & Eric Carrasco

Official Description: JAMES CONSIDERS UNMASKING AS GUARDIAN – When Tanya, a disciple of Coville’s, escapes from what’s left of his cult, she gives Kara and James a journal that could hold the key to saving Sam. Someone learns Guardian’s identity and threatens to expose James if he doesn’t do what they ask. James contemplates what it means to be a black vigilante without a mask in America.

Reoccurring Cast:

Guest Stars: Thomas Coville (Chad Lowe) | Tanya (guest star Nesta Cooper)

Special Notes:

spoilers season3 episode18Title: Shelter From The Storm

Directed By: Antonio Negret

Air Date: May 14th, 2018

Story By: Robert Rovner

Teleplay By: Lindsay Gelfand & Allison Weintraub

Official Description: REIGN SETS HER SIGHTS ON RUBY – When Reign starts hunting Ruby, Supergirl and Alex work together to keep her safe. Supergirl and J’onn look to Sam’s mother for advice on how to stop Reign and come away with some shocking news.

Reoccurring Cast: Ruby (Emma Tremblay)

Guest Stars: Patricia Arias (Betty Buckley)

Special Notes:

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spoilers season3 episode17Title: Trinity

Directed By: Caitlin Parrish & Erica Weiss

Air Date: May 7th, 2018

Story By: Jessica Queller

Teleplay By: Caitlin Parrish & Derek Simon

Official Description: SUPERGIRL TAKES ON ALL THREE WORLDKILLERS – Still reeling after learning about Lena’s secret, Supergirl asks Guardian for a favor that could alter his relationship with Lena forever. Meanwhile, with all three Worldkillers united, Supergirl and the team brace for an epic battle.

Reoccurring Cast:

Guest Stars:

Special Notes:

spoilers season3 episode16Title: Of Two Minds

Directed By: Alexandra La Roche

Air Date: April 30th, 2018

Written By: Gabriel Llanas & Anna Musky-Goldwyn

Official Description: SUPERGIRL AND IMRA MUST WORK TOGETHER TO STOP THE THIRD WORLDKILLER – Supergirl and Imra have different ideas on how to stop the third Worldkiller, Pestilence. However, when both Alex and Winn are seriously injured by Pestilence, Supergirl and Imra team up to stop the destruction.

Reoccurring Cast: Imra (Amy Jackson)

Guest Stars: 

Special Notes: Also, according to set photos, it looks like Mon-El will be adorning the famous red suit again this episode! See below:

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spoilers season3 episode15Title: In Search of Lost Time

Directed By: Andi Armaganian

Air Date: April 23rd, 2018

Story By: Eric Carrasco

Teleplay By: Katie Rose Rodgers & Nicki Holcomb

Official Description: When M’yrnn inadvertently causes psychic disturbances at the DEO, Supergirl must work with J’onn to contain the resulting chaos. Meanwhile, Mon-El begins training Kara in fighting techniques he’s learned in the future for battling Worldkillers.

Reoccurring Cast:

Guest Stars: M’yrnn J’onzz (Carl Lumbly) | Finhead (Rochelle Okoye) | Mary McGowan (Laurie Metcalf) unconfirmed | Mandrax (Paul Lazenby)

Special Notes: According to production schedule, the show was likely filming episode 315 at the time when Chris Wood posted this to his instagram. This could be the first time on the show we see his iconic uniform.

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spoilers season3 episode14Title: Schott Through The Heart

Directed By: Glenn Winter

Air Date: April 16th, 2018

Written By: Caitlin Parrish & Derek Simon

Official Description: OSCAR-NOMINATED ACTRESS LAURIE METCALF GUEST STARS – When Winn’s father dies, his estranged mother, Mary, reappears trying to reconnect and to explain why she abandoned him all those years ago. Winn is too embittered from his rough childhood to forgive her but when a copycat Toyman attacks, the two must work together to stop him. Mon-El tells Kara something important about the Worldkillers, and Alex becomes suspicious of M'yrnn’s recent behavior.

Reoccurring Cast:

Guest Stars: Mary McGowan, Winn's Mother (Laurie Metcalf) | (Brooke Smith) | M'yrnn (Carl Lumbly)

Special Notes: The death of the original Toyman shocks Winn Schott and his friends. However, that isn't the last prank he is looking to play. At his funeral, a bomb goes off where his casket becomes a true instrument of death! Winn's mother, played by Laurie Metcalf arrives to comfort her son finally after years of fear. She has been told that if she ever approached Winn, he would be killed via the Toyman. Whether the Toyman is dead or not, killer toys are released on National City and only Supergirl can save them all. A successor to the Toyman is revealed to be  played by Brooke Smith. Winn's mother's motivations are still in question and while Jacqueline might be the target for Supergirl's might, the Toyman's legacy remains to be expunged!

spoilers season3 episode13Title: Both Sides Now

Directed By: Jesse Warn

Air Date: February 5th, 2018

Written By: Jessica Queller & Paula Yoo

Official Description: THE DEO CAPTURES ANOTHER WORLDKILLER – The DEO captures a second Worldkiller, Purity. Supergirl and Alex use very different methods of interrogation with Purity in the hopes of finding out how to defeat Reign. However, Purity escapes and attacks the city’s subway tunnels. Meanwhile, J’onn, Winn and Mon-El band together to fix the Legion ship.

Reoccurring Cast:

Guest Stars: Purity (Krys Marshall)

Special Notes: has a decent introductory article on Purity and what a second Worldkiller will mean for the girl of steel.

spoilers season3 episode12Title: For Good

Directed By: Tawnia McKiernan

Air Date: January 29th, 2018

Story By: Robert Rovner

Teleplay By: Cindy Lichtman & Alix Sternberg

Official Description: MORGAN EDGE THREATENS LENA – Someone tries to kill Morgan Edge and he barely survives. He accuses Lena of being behind the attempt and vows to destroy her. When Lena fears her hatred for Morgan will take her to the Luthor dark side, Kara steps in to help her friend. Meanwhile, after Sam realizes she’s losing time, she confides in Alex who decides to run some medical tests to see if she can find out what’s going on with her new friend

Reoccurring Cast:

Guest Stars: Morgan Edge (Adrian Pasdar)

Special Notes: 

spoilers season3 episode11Title: Fort Rozz

Directed By: Gregory Smith

Air Date: January 22nd, 2018

Written By: Gabriel Llanas & Anna Musky-Goldwyn

Official Description: SUPERGIRL TEAMS UP WITH SATURN GIRL, LIVEWIRE AND PSI – As Reign continues to terrorize the city, Supergirl teams up with Saturn Girl, and the two recruit Supergirl’s former enemies, Livewire and Psi, to form a team for a mission to Fort Rozz to recover a prisoner who has information on how to defeat Reign once and for all. Meanwhile, Alex babysits Ruby.

Reoccurring Cast: Saturn Girl (guest star Amy Jackson)

Guest Stars: Erika (Vanessa Przada) | Livewire (Brit Morgan) | Psi (Yael Grobglas)

Special Notes: A new guest star shows up this episode named Erika, and played by Vanessa Przada. What exactly her role will be is unknown but it sounds like there is potential for more episodes.

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spoilers season3 episode10Title: The Legion of Superheroes

Directed By: Jesse Warn

Air Date: January 15th, 2018

Written By: Derek Simon & Eric Carrasco

Official Description: MEET THE LEGION – Struggling to heal from her injuries inflicted by Reign, Supergirl remains in a dreamlike state, unable to be reached. Mon-El recruits one of the Legion members, Brainiac-5, to try to bring her back. Meanwhile, Reign continues her rampage on the city so the DEO teams up with the Legion of Superheroes to try to stop her.

Reoccurring Cast:

Guest Stars: Brainiac 5 (Jesse Rath) | Saturn Girl (Amy Jackson)

Special Notes: In a radio interview that Amy Jackson did with BBC, she noted that the Legion would be utilizing their flight rings, as well as "suiting up" meaning that we should get to see Saturn Girl, Mon-El and Brainiac 5 all in their Legion costumes at some point this episode!

spoilers season3 episode9Title: Reign

Directed By: Glen Winter

Air Date: December 4th, 2017

Written By: Paula Yoo & Caitlin Parrish

Official Description: REIGN CHALLENGES SUPERGIRL – Supergirl investigates a mysterious symbol popping up all over National City, tracing its origins back to an ancient prophecy and the mark of the World Killer, Reign. Meanwhile, the tension between Lena and Morgan Edge continues to build, causing James to step in and offer up some protection, and possibly igniting a spark in the process.

Reoccurring Cast:

Guest Stars: Saturn Girl (Amy Jackson) | Morgan Edge (Adrian Pasdar)

Special Notes: It looks like this episode will welcome back Amy Jackson as Saturn Girl.

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spoilers season3 episode8Title: Crisis on Earth X Part 1

Directed By: Larry Teng

Air Date: November 27th, 2017 8pm The CW

Story By: Andrew Kreisberg & Marc Guggenheim

Teleplay By: Robert Rovner & Jessica Queller

Official Description: THE EPIC FOUR-WAY CROSSOVER WITH “ARROW,” “SUPERGIRL,” “THE FLASH” AND “DC’S LEGENDS OF TOMORROW” BEGINS — Barry and Iris’s wedding brings the gang together, but things go awry when villains from Earth-X attack the ceremony. All of the superheroes band together with help from their super friends like Citizen Cold, The Ray, Felicity Smoak, Iris West and Alex Danvers to take on their most formidable villains yet. Earth’s mightiest heroes – Green Arrow, Supergirl, The Flash and White Canary – lead their teams into battle to save the world.

Reoccurring Cast:

Guest Stars: Barry Allen (Grant Gustin) | Iris West (Candice Patton) | Citizen Cold (Wentworth Miller) | The Ray (Russell Tovey) | Felicity Smoak (Emily Bett Rickards) | Green Arrow (Stephen Amell) | White Canary (Caity Lotz)

Special Notes: This is the first episode of the "True" 4 show crossover event that will feature all four Arrowverse shows. It starts with Supergirl and is followed by a special episode of Arrow that same night. The crossover is concluded on Tuesday November 28th, 2017 at 8pm via The Flash and Legends of Tomorrow.

Of the Supergirl cast rumored to be featured in the crossover, we have heard that Winn, Alex and Kara will be featured and Alex and Kara will be in all four episodes. Alex and Sara Lance (from legends) are rumored to share at least two scenes. There will be a scene with just Iris, Kara and Felicity as well.

spoilers season3 episode7Title: Wake Up

Directed By: Chad Lowe

Air Date: November 20th, 2017 8pm The CW

Written By: Gabriel Llanas & Anna Musky-Goldwyn

Official Description: When Winn and the team discover an alien ship has crash landed deep underwater beneath National City, Kara/Supergirl is called in to investigate. Meanwhile, Hank attempts to bond with his father, M'yrnn. Samantha, eager for some understanding of the changes she has been experiencing, looks to her estranged mother, Patricia Arias, for answers.

Reoccurring Cast:

Guest Stars: Saturn Girl (Amy Jackson) | Patricia Arias (Betty Buckley) | M'yrnn (guest star Carl Lumbly)

Special Notes: Rumors are going about that Mon-El will return this episode but things will be different. Betty Buckley will make her first appearance on the show as well as Samantha's adoptive mother. Her character is described as:

Patricia [Arias] is Samantha Arias' (Odette Annable's) adoptive mother. Patricia is honest, but stubborn. She and Samantha have been estranged for many years, the result of Samantha getting pregnant as a teenager. Their troubled relationship is made all the more complex by the secrets Patricia holds.

spoilers season3 episode6Title: Midvale

Directed By: Rob Greenlea

Air Date: November 13th, 2017 8pm The CW

Written By: Caitlin Parrish & Jess Kardos

Official Description: Kara and Alex head home to Midvale for a little R&R. While there, Kara recalls a painful memory of a childhood friend’s death and how that traumatic experience brought the Danver sisters closer together. Izabela Vidovic plays Young Kara and Olivia Nikkanen plays Young Alex in flashbacks.

Reoccurring Cast: Eliza Danvers (Helen Slater)

Guest Stars: Olivia Nikkanen (Teenaged Alex) | Izabela Vidovic (Teenaged Kara) | Josie (Eliana Jones) | (Mik Byskov) |

Special Notes: This episode is going to be a big flashback to Midvale High. Heavy with amazing sister action, we'll get to see how the girls were getting through high school, including a scene with the girls fighting over bathroom time and a hair straightener. Kara and Alex will set aside their differences in popularity to uncover a mystery unfolding at their school that resulted in the death of a student (a character named Kenny) and the injury of another (named Mark), as well as a conspiracy held by their teacher, Mr. Bernard. Josie, Alex's friend who views Kara as an unpopular dork, holds a clue to Mr. Bernard's secret in a trade for a good recommendation letter to Berkley. What Mr. Bernard is up to and just how Kara and Alex will solve the case is still unfolding!

spoilers season3 episode5Title: Damage (Originally titled Two Rings)

Directed By: Kevin Smith

Air Date: November 6th, 2017 8pm The CW

Written By: Eric Carrasco & Cindy Lichtman

Official Description: When multiple children get sick from lead poisoning, Morgan Edge points the finger at Lena  and blames her creation of the lead bomb she made to save National City from the Daxamites. While Lena knows she never intended any harm, she fears there may have been a flaw in her design, leaving her responsible. Kara teams up with Samantha to clear Lena’s name, but it turns out to be harder than they thought. Meanwhile, Alex and Maggie make a crucial decision about the future of their relationship.

Reoccurring Cast: Maggie Sawyer (Floriana Lima)

Guest Stars: Morgan Edge (Adrian Pasdar)

Special Notes: Rumors are that this will be the last episode for Floriana Lima's Maggie unless her schedule allows for her to return. Tertiary sources have claimed an amicable break-up could be in store for Alex and Maggie. Circumstances are unknown and this is still filed under rumor.

spoilers season3 episode4Title: The Faithful

Directed By: Jesse Warn

Air Date: October 30th, 2017 8pm The CW

Written By: Paula Yoo & Katie Rose Rogers

Official Description: Kara investigates a secretive new group whose leader, Thomas Coville, has a mysterious connection to Supergirl. Meanwhile, Samantha feels like she’s letting Ruby down, and J’onn confesses an old secret.

Reoccurring Cast: Maggie Sawyer (Floriana Lima)

Guest Stars: Olivia (unknown) | Thomas Coville (Chad Lowe) | Ruby Arias (Emma Tremblay

Special Notes: A character named Olivia will play a part in this episode. She was saved by Supergirl after attempting suicide when she found out her boyfriend was cheating on her. This save will end up being transformative for her and she'll end up going to a support group that allows others saved by Supergirl to gather and discuss how they were saved. The tone of the group is almost religious in nature and its still up in the air if this will be good, or bad for the Girl of Steel.

The leader of the cult is Thomas Coville played by Chad Lowe (director of episode 307). His character is described as:

Thomas Coville, a charismatic religious leader with a surprising connection to Supergirl — his cult basically worships the Girl of Steel. He’s a deeply spiritual man, committed to preaching his faith and transforming his followers’ lives

James will share a story about the time when he first met Superman and Andrew Kreisberg has gone on record saying it was the one of his most favorite things he's read from the show!

spoilers season3 episode3Title: Far From The Tree

Directed By: Dermott Downs

Air Date: October 23rd, 2017 8pm The CW

Written By: Jessica Queller & Derek Simon

Official Description: CARLOS BERNARD (“24”) GUEST STARS; HELEN SLATER RETURNS — Eliza throws Alex and Maggie a wedding shower, which causes Maggie to reach out to her estranged father. Supergirl joins J’onn on a personal mission.

Reoccurring Cast: Maggie Sawyer (Floriana Lima)

Guest Stars: Oscar Rodas (Carlos Bernard) | M’yrnn J’onzz (Carl Lumbly) | Da'rack (Unknown) | M'Gann M'orzz (Sharon Leal*) | Eliza Danvers (Helen Slater)

Special Notes: It's a Martian episode! Actually there is a lot in this one. Maggie Sawyer and Alex Danvers are thrown a wedding shower at Kara's apartment. The newly engaged couple, however, certainly have their difficulties with their fathers and wouldn't you know it, Maggie's father, a fellow cop named Oscar Rodas played by (Carlos Bernard) shows up. Meanwhile another father shows up in the mix, J'onn J'onzz's father, M'yrnn played by (Carl Lumbly). A mysterious White Martian is also in the mix named Da'rack who is inspired by M'Gann's resistance movement on on Mars. *M'Gann is rumored to appear this episode.

spoilers season3 episode2Title: Triggers

Directed By: David McWhirter

Air Date: October 16th, 2017 8pm The CW

Written By: Gabriel Llanas & Anna Musky-Goldwyn

Official Description: Psi, a thief with psychic powers, attacks National City. Able to immobilize people by tapping into their worst fears, Psi proves a formidable opponent for Supergirl. Meanwhile, James and Lena are at an impasse, and Samantha starts her new job at L-Corp.

Reoccurring Cast: Maggie Sawyer (Floriana Lima)

Guest Stars: Psi (Yael Grobglas) | Ruby Arias (Emma Tremblay) | M'Gann M'orzz (Sharon Leal)

Special Notes: Bank robbing never felt so easy when you have the psychic abilities of the villainous Psi. Yael Grobglas will ravage National City and Supergirl's mind in episode 302.

spoilers season3 episode1Title: Girl of Steel

Directed By: Jesse Warn

Air Date: October 9th, 2017 8pm The CW

Story By: Andrew Kriesberg

Teleplay By: Robert Rovner & Caitlin Parrish

Official Description: "Dream a little dream of you" Kara deals with the loss of Mon-El by focusing all her energy on being Supergirl and the mysterious new threat against National City. Alex confesses a secret to Maggie about their impending nuptials. A citizen of National City has a mysterious connection to Kara, and Lena makes a bold move.

Reoccurring Cast: Morgan Edge (Adrian Pasdar) | Ruby Arias (Emma Tremblay) | Maggie Sawyer (Floriana Lima)

Guest Stars: Cat Grant (Calista Flockhart)

Special Notes: National City celebrates Supergirl's defeat of the Daxamite invasion! However during a reveal of a Supergirl statue presented by Lena Luthor herself, a disastrous missile attack occurs orchestrated by Morgan Edge and carried out by Robert Dubios aka Bloodsport! Reign aka Samantha March will be in attendance with her daughter Ruby during the attack. With Supergirl otherwise engaged in saving the day Samantha will have no choice but to expose her powers to save her daughter from the falling statue. Lena will call out Morgan on the attack but won't be able to prove it which will give Lena "all of Morgan's attention". Supergirl, continued to be troubled by the loss of Mon-El debates what it is to be human and dives deeper into her Kryptonian personality Supergirl, all but abandoning Kara Danvers. Finally, a shake up at Catco will force leadership roles to possibly change and despite Cat's return last season, James will remain in the drivers seat at Cat Co.

Reign has been on Earth for a while, possibly longer than Kara. (rumor).

Reign has a daughter named Ruby March. Reign tries to hide her powers from her daughter and everyone else but is forced to use them to save her daughter when an accident happens and a statue falls on top of Ruby.

Calista Flockhart will attempt to make more appearances in the show while still remaining a guest star.

Lena Luthor and Reign are going to have an "unexpected connection" According to Jessica Queller

Character Descriptions Via Casting Calls:

ROBERT DUBOIS/BLOODSPORT – Male, 30-40s…Looking for memorable, and distinctive performers. This evil and threatening Merc is an ex-military man who has infiltrated his former base and stolen a variety of articles that he uses to cloak an underwater nuclear device. As we later learn, he is in the employ of Morgan Edge, and he has been hired to blow up the waterfront with an underwater nuke…PRINCIPAL

SAMANTHA ARIAS/REIGN – Female, late 20s to early 30s. Diverse. Samantha is a professional, young single mom (Trying to balance work and life), who begins to struggle to hold onto her humanity when an alter-ego, Reign — ruthless, righteous, superhuman — begins to take over her personality. Most important in Sam’s life is her young daughter, Ruby, who Sam would sacrifice everything to protect. ONE SEASON – FRACTIONAL SERIES REGULAR.

RUBY ARIAS – Female, Caucasian or Latina, 11 to 14. Smart, sensitive, funny, but a bit of an outsider with her peers. An independent think who doesn’t like to follow the crowd. She’s fiercely loyal to her single mother, Sam (Odette Annable) and the two make a great team, looking out for each other and enjoying each other’s camaraderie. But Ruby’s not shy about speaking up for herself – even to her mother – when she feels she’s in the right. MAJOR RECURRING GUEST STAR THIS SEASON WITH A SERIES REGULAR OPTION FOR NEXT SEASON.

GAIL MARSH – Female, Late 20s, early 30s, Open Ethnicity. The deadly and seductive PSI (aka Gail Marsh), a DC Comics foe of Supergirl, possesses psychic abilities which allow her to bring out her victim’s darkest fears. While she is a physical threat, her real power comes in bringing the Girl of Steel to her knees without throwing a punch. LEAD GUEST STAR

MORGAN EDGE – Male, 40s, Open Ethnicity. As corrupt as he is intimidating, he intends to clear the area one way or another, and he has enlisted the services of a madman to blow up the area during a special ceremony in Supergirl’s honor. This savvy and formidable titan of industry is pushing through a huge new redevelopment plan for the city’s waterfront – and he doesn’t care if he has to uproot the entire indigenous immigrant population to implement his money-grubbing scheme. …RECURRING GUEST STAR

Maggie Sawyer does not die, as confirmed in an article from Entertainment Weekly. Executive Producer Andrew Kreisberg said:

Maggie does not die. I’m sure a lot of people are afraid of that. Maggie will continue to exist in the world and we hope that if the opportunity presents itself for her, that she’ll come back from time to time. Unfortunately, Floriana decided to move on, which left us with, how do we write her out as a regular while still honoring these two women who were deeply in love with each other? Taking a page out of some of our own personal dating history, we’ve come up with a story that we really feel like honors what’s come before them, and honors how much they love each other, how much they mean to each other, and how much they’ve changed each other’s lives. It’s some of the most emotional stuff we’ve ever done, and Floriana has been so good in these first five episodes. Episode 3 is all about Maggie and her dad, played by Carlos Bernard, and it’s some of the most heartbreaking stuff I’ve ever done on anything I’ve ever done.

Kara and Lena will have many more adventures as the season begins. In a spoiler room article, Entertainment Weekly spoke to Executive Producer Andrew Kreisberg who said:

Lena and Kara’s friendship will continue to grow. There’s a lot of Lena-Kara adventures early on in this season. The most interesting thing about Lena is that she is so good, and so moral, and believes in second chances, but she comes from this family of truly evil people. As people are going to realize over the course of this season, it doesn’t take much to make you bad. People don’t just turn evil. They do one small bad thing and then that leads to another, and then to another, and so any time you’re watching Lena, you’re always wondering, ‘Is this the moment when she does the one small thing?'

According to another Entertainment Weekly Spoiler Room, Katie McGrath says she is going to go some lengths to help Kara in her time of need after Mon-El's departure:

While Lena’s feeling good that she helped saved the world, she feels very responsible that her best friend is hurting, and she’s trying to bring Kara back to the friendship that they had.

Katie went on to tease that Lena will do something very big in the premiere to try to rectify that.

According to TV Guide, Reign's story will be a dividing one for team Supergirl. Expect these three things for season three:

  1. She's a ticking time bomb. The season finale showed Reign being sent to Earth from Krypton as an infant. She was genetically created on that planet to be a weapon of mass destruction, executive producer Andrew Kreisberg says. "But she has no idea! She has been living in National City as [a now grown-up] person named Samantha Arias."
  2. She is breaking the Arrowvers's "evil" mold. "One thing we've never done on Arrow or The Flash is watch the villain become the villain," Kreisberg says. "Sam is just Sam." But as the season progresses, the working single mom "will realize there is something different about her", Kreisberg continues. "It's a fun dark-mirror version of the journey Christopher Reeve took in the original Superman as Clark".
  3. She'll divide the team. Sam will develop connections with Supergirl's core characters which will cause friction down the road. "Everyone will have a relationship with her, and that will drive much of the season in terms of how far they're willing to go to stop her when she becomes Reign", Kreisberg explains. "Some will believe she need to be saved; others will think she needs to be stopped."

At Comic Con 2017 this year Melissa told us that Supergirl's costume wouldn't change, however, according to a recent spoiler room from Entertainment Weekly, we will see her is something different for a time.

There is a different suit that I will be wearing at some point this season, but I won’t tell you when or to what capacity, It’s cool, though.