Invasion (Guardian Arrowverse)

Invasion is the name of the third annual Guardian Arrowverse crossover event. Due to the event going over four separate series, it's condensed into a five-act film.

Summary
When a race of alien creatures called Dominators arrive on Earth, Team Flash recruit their friends to stand against them. When their true motive, to destroy all Meta-Humans, is revealed, Barry must make a tough choice to either surrender himself or stand with his friends and fight. Heroes from across the multiverse and even time come together in an epic crossover event.

Main

 * Melissa Benoist as Kara Zor-El/Kara Danvers/Supergirl: The younger biological twin of Alexa Sparks and younger adoptive sister of Alex Danvers and the superheroine known as Supergirl. She was born on the planet Krypton and currently lives in National City on Earth-38.
 * Lucy Hale as Xera Zor-El/Alexandra "Alexa" Sparks/Angel: The older biological twin of Kara Danvers and older adoptive sister of Emily Sparks and the superheroine known as Angel. She was born on the planet Krypton and currently lives in National City on Earth-38.
 * Holland Roden as Sol-Gon/Emily Sparks/Solaris: The older biological sister of Elizabeth Mendel and the younger adoptive sister of Alexa Sparks and the superheroine known as Solaris. She was born on the planet Drakonia and currently lives in National City on Earth-38 and is the girlfriend of Dr. Harrison Chambers.

Recurring

 * Tom Cavanagh as Dr. Harrison Chambers: The Earth-38 doppelganger of Harrison Wells who's a research scientist employed at D.E.O (Department of Extra-Normal Operations) and is the boyfriend of Emily Sparks.

Main

 * Holland Roden as Sei-Gon/Elizabeth Mendel/Mother Nature: The true heir of the Drakonian Royal family and youngest sister of Emily Sparks of Earth-38. She goes by the codename Mother Nature and is the second-in-command of Central City's Team Flash.
 * Troian Bellisario as Det. Lorelai Snart/Ice Princess: One of Elizabeth's five Guardians, who wields the power of the Bear's Head Animal Gem. She goes by the codename Ice Princess and is a member of Central City's Team Flash. She is also the girlfriend of Cisco Ramon/Vibe.
 * Grant Gustin as Barry Allen/The Flash: The leader of Central City's Team Flash and the hero who unites the various teams against the Dominators. He goes by the codename The Flash and harbors feelings for his teammate Claire Daniels/Carbuncle.
 * Dianna Agron as Dr. Claire Daniels/Carbuncle: One of Elizabeth's five Guardians, who wields the power of the Carbuncle Animal Gem. She goes by the codename Carbuncle and is a member of Central City's Team Flash as well as one of their medical professionals. Despite being in a relationship, Claire still harbors strong feelings for Barry Allen/The Flash.
 * Carlos Valdes as Cisco Ramon/Vibe: The mechanical genius and tech guru of Central City's Team Flash who's powers include dimensional awareness and the ability to open breaches between Earths. He goes by the codename Vibe and is the boyfriend of Lorelai Snart/Ice Princess. It's revealed in the epilogue that he plans on proposing to Lorelai with a ring given to him by his grandmother.

Recurring

 * Danielle Panabaker as Dr. Caitlin Snow/Killer Frost: A bio-engineer and the other medical professional of Central City's Team Flash who's suppressing her cryo-powers with a pair of meta dampening cuffs.
 * Candice Patton as Iris West: The best friend of Barry and Claire, the daughter of Joe, older sister of Wally, and the girlfriend of Theo. She is also a member of Central City's Team Flash.
 * Paul Wesley as Theo Daniels: The older brother of Claire and boyfriend of Iris. He is also a member of Central City's Team Flash.
 * Jesse L. Martin as Det. Joe West: The father of Iris and Wally, foster father of Barry, and surrogate father of Claire and Lorelai, as well as the latter's partner at the Central City Police Department. He is also a member of Central City's Team Flash.
 * Tom Cavanagh as H.R Wells: The Earth-19 doppelganger of Harrison Wells and a member of Central City's Team Flash.
 * Keiynan Lonsdal as Wally West/Kid Flash: The son of Joe, younger brother of Iris, foster brother of Barry, and the hero known as Kid Flash. He is also a member of Central City's Team Flash.

Main

 * Vanessa Morgan as Selena Merlyn-Rayne/Lunar Wolf: One of Elizabeth's five Guardians as well as their leader who wields the power of the Wolf's Paw Animal Gem. She goes by the codename Lunar Wolf and is the second-in-command of Star City's Team Arrow. She is also the wife of Rachel Rayne-Merlyn/Oracle.
 * Stephen Amell as Oliver Queen/Green Arrow: The Mayor of Star City as well as the leader of Team Arrow, going by the codename Green Arrow. His partner in the field is Andrea Rayne/Arctic Fox, whom he still has strong romantic feelings for.
 * Nina Dobrev as Andrea Rayne/Arctic Fox: The Star City District Attorney, second-in-command of Team Arrow, and one of Elizabeth's five Guardians, who wields the power of the Fox Head Animal Gem. She goes by the codename Arctic Fox and is the field partner of Oliver Queen/Green Arrow, whom she still has strong romantic feelings for.
 * Cassie Scerbo as Elena Queen/Thunder Eagle: The younger sister of Oliver and older sister of Thea, a member of Star City's Team Arrow and one of Elizabeth's five Guardians who wields the power of the Eagle's Head Animal Gem. She goes by the codename Thunder Eagle and is the field partner of Selena Merlyn-Rayne/Lunar Wolf and is also the best friend of Lorelai Snart/Ice Princess. During the epilogue, Cisco confides in Elena that he's going to propose to Lorelai.
 * Dove Cameron as Rachel Rayne-Merlyn/Oracle: The hacker for Star City's Team Arrow and the younger sister of Andrea Rayne/Arctic Fox. She goes by the codename Oracle and is also the wife of Selena Merlyn-Rayne/Lunar Wolf.
 * David Ramsey as John Diggle/Spartan: A member of Star City's Team Arrow, the best friend of Oliver Queen/Green Arrow and the husband of A.R.G.U.S Director, Lyla Michales. He goes by the codename Spartan.
 * Willa Holland as Thea Queen-Drake/Speedy: The youngest sister of Oliver Queen/Green Arrow and Elena Queen/Thunder Eagle and the wife of Tim Drake/Robin. She was once retired but came back to Team Arrow when she heard about the alien invasion, taking up her old mantle Speedy.
 * Dylan O'Brien as Tim Drake/Robin: A member of Star City's Team Arrow who came out of retirement once he heard about the alien invasion, taking up his old mantle Robin. He is also the husband of Thea Queen-Drake/Speedy.

Recurring

 * Liam Neeson as Hu-Or: A Drakonian elder and paternal uncle of Emily Sparks and Elizabeth Mendel who also trained Selena Merlyn-Rayne/Lunar Wolf and told her about the Guardians and gave her the Animal Gems. He shows up to aid the Guardians in unlocking their Animal Auras to use in the battle against the Dominators.
 * Audrey Marie Anderson as Lyla Michales: The director of A.R.G.U.S and wife of John Diggle/Spartan.
 * Echo Kallum as Curtis Holt/Mr. Terrific: The tech expert and member of Star City's Team Arrow, going by the codename Mr. Terrific. His primary field partner is Rory Reagan/Ragman.
 * Rick Gonzalez as Rene Ramirez/Wild Dog: A member of Star City's Team Arrow who goes by the codename Wild Dog. His primary field partner is Karina Knyazev/Salem, who it's hinted he's romantically attracted to.
 * Alexandra Daddario as Karina Knyazev/Salem: A member of Star City's Team Arrow as well as their medical professional. She's a meta-human with cat like reflexes and instincts as well as hyper regeneration. She goes by the codename Salem. Her primary field partner is Rene Ramirez/Wild Dog, who it's hinted she's romantically attracted to.
 * Joe Dinicol as Rory Reagan/Ragman: A member of Star City's Team Arrow who goes by the codename Ragman. His primary field partner is Curtis Holt/Mr. Terrific.

Legends of Tomorrow

 * Victor Garber as Professor Martin Stein/Firestorm: A physicist and member of the time-traveling Legends and one half of the meta-human known as Firestorm.
 * Brandon Routh as Ray Palmer/The Atom: Former CEO of Palmer Technologies and a member of the time-traveling Legends. He goes by the codename The Atom and uses an exosuit powered by a dwarf star alloy.
 * Caity Lotz as Sara Lance/White Canary: Former member of the League of Assassins and the leader of the time-traveling Legends, going by the codename White Canary. She is good friends with the members of Team Arrow.
 * Sophia Bush as Ro-Aon/Rowan Eon/Tempus: A Drakonian and former Time Master, and a member of the time-traveling Legends. She goes by the codename Tempus and has the power to manipulate time itself on certain levels. She helps Emily and Elizabeth hone their own Drakonian powers.
 * Franz Drameh as Jefferson "Jax" Jackson/Firestorm: A mechanic and member of the time-traveling Legends and one half of the meta-human known as Firestorm.
 * Maisie Richardson-Sellers as Amaya Jiwe/Vixen: Former member of the JSA and member of the time-traveling Legends. She wields the power of the Anansi Totem and goes by the codename Vixen.
 * Nick Zano as Dr. Nate Heywood/Steel: A historian and member of the time-traveling Legends, who has the power to transform his body into organic steel, going by the codename Steel. It's also hinted he's romantically attracted to Rowan/Tempus.
 * Dominic Purcell as Mick Rory/Heatwave: A former criminal arsonist and member of the time traveling Legends, who goes by the codename Heatwave. As a way to honor his late partner, Leonard Snart/Captain Cold, Mick keeps an eye on Lorelai Snart/Ice Princess and treats her like a kid sister.

Acts
* Indirectly related episode

Misc. Trivia

 * An alternative title for this crossover was Heroes vs Aliens.
 * This is the first crossover event to include characters from the Supergirl show and the Legends of Tomorrow based series
 * Due to the large cast and different stories, this crossover will be posted to FanFiction.net as a separate entity with five parts.
 * This will be the case with the following crossovers: Crisis on Earth-X/Rise of The Guardians, Elseworlds, and Crisis on Infinite Earths.

Prologue: The First Invasion

 * This describes (via voiceover) and details the first invasion of the Dominators in Redmond, Oregon during 1951. The event will be further explored in Invasion Part 3.
 * There's a mention of other worlds the Dominators have visited, two of which are Krypton and Drakonia.
 * Krypton being the home planet of Kara Zor-El/Kara Danvers and Xera Zor-El/Alexandra Sparks.
 * Drakonia being the home planet of Emily Sparks, Elizabeth Mendel, and Ro-Aon/Rowan Eon.