|"Things were looking a little grim, but part of me was, admittedly, a little excited for a "reunion" of old friends."|
- For other uses of "Invasion!", see Invasion! (disambiguation)
- "There's Flash and—and Supergirl and—and people with actual powers now. Whatever needs to be done, they can handle it. We—we finally have a chance to be happy. I mean, why—why can't you just for a second accept that maybe this is your reward for all of the sacrifices you have made?"
- —Thea Queen to Oliver Queen
The episode is the third of the four-part crossover, , with the eighth episode of the second season of , the eighth episode of the third season of and the seventh episode of the second season of .
Oliver wakes up to a life where he never got on The Queen's Gambit. Robert and Moira are alive and well. Laurel is his loving fiancée and their wedding is imminent. Everything seems perfect, but Oliver starts to notice small imperfections that make him question this new reality. Meanwhile, Felicity and the recruits take on a new threat with help from The Flash and Supergirl.
- This is the first episode of the series to not feature Josh Segarra (Adrian Chase) after signing on as a series regular.
- When mentioning how they have to find "Oliver and company", Cisco makes it clear that he is not referring to the 1988 Disney film Oliver & Company that was inspired by the novel Oliver Twist.
- This is the first episode of Season 5 that doesn't include the flashback storyline.
- The beginning of the episode, when Oliver is running, is a reference to the first scene of the very first episode of (and the Arrowverse), "", a trend that continued at the start of every Arrow season's first episode except Season 5.
- This is the first appearance of Sara on since "", and the first appearance of Ray on Arrow since "".
- This episode marks Deathstroke's first appearance since "". However, he wasn't shown without his mask and didn't say a word, due to Manu Bennett not reprising the role.
- However Deathstroke can briefly be seen without his mask in Thea's flashback from "".
- Cisco refers to the stasis that the heroes are being kept in as "a little alien, a little Star Trek - J. J. Abrams style", referring to the 2009 film, Star Trek, and its 2013 sequel Star Trek Into Darkness, both of which were directed by J. J. Abrams.
- Evelyn Sharp neither appears nor is even mentioned in this episode.
- This episode marks Susanna Thompson's first appearance as Moira Queen since Season 2's "" (57 episodes ago) and Jamey Sheridan's first appearance as Robert Queen since Season 3's "" (40 episodes ago).
- In the beginning of the episode, Oliver asks Laurel, "Will you marry me?" Laurel shows him her engagement ring and responds, "I think I already answered that question." This dialogue is copied from the Season 4 episode "" from Oliver and Felicity's conversation at the end.
- The bow Cisco used to track down Oliver is the bow Oliver used in the first season.
- The Hōzen Thea gave to Oliver as a gift is the same Hōzen Oliver gave Thea after he returned from Lian Yu in "".
- This is the second episode in which Barry appears only as The Flash. The first one is "".
- Curtis refers to his "3PO processor", before imitating C-3PO from the Star Wars franchise.
- Ra's al Ghul and Prometheus are the only main antagonists of (from the Present storyline) who didn't appear in the dream world. However, Ra's al Ghul briefly appeared in Sara's flashback from "".
- Firestorm makes a cameo at Sara's flashback from the previous part of the crossover, "". This marks the first time since "" that Firestorm appears without Martin Stein/Jefferson Jackson/Ronnie Raymond.
- Curtis claims to feel like "Elliott from E.T.", exclaiming "It's working, it's working!", quoting the protagonist from the 1982 film, E.T. the Extra-Terrestrial.
- Ray jokingly suggests they "click [their] heels three times and say there's no place like home" to escape the dream world, a reference to The Wizard of Oz.
- As the 100th episode of , this episode included clips from different episodes through the series.
- The bartender "Joe", who gives drinks to Laurel and Sara at the rehearsal dinner, is played by the real-life father of Caity Lotz.
- Laurel and Quentin are shown drinking alcohol in the dream world, indicating they never became alcoholics in that reality.
- In the dream world, Tommy was stated to be a doctor in Chicago. This is a reference to Colin Donnell's role in Chicago Med, where he plays the role of a doctor. Furthermore, this was the reason that he could not return for a full appearance. However, his image was digitally inserted during the scene where Oliver returns to the real world, much to Colin Donnell's surprise.
- Donnell posted on Twitter stating that although he did not appear, he had seen the episode weeks ago and praised the scene between Oliver and Thea and gave kudos to his Chicago Med reference.
- Felicity and Ray are revealed to be engaged in the dream world, just as they were together in the third season.
- As the heroes fight the villains in the dream world, there are throwbacks to earlier in the series, or characters gain some form of closure.
- Sara kills Damien Darhk in the same manner that he killed her sister, Laurel; thrusting an arrow into his stomach.
- Oliver kills Deathstroke, who killed his mother, by shooting an arrow into his eye, just as he did with the real Slade Wilson.
- John Diggle fights a Ghost, which is what his brother, Andy, became.
- Ray kills a member of Slade Wilson's army, who killed his fiancée, Anna Loring.
- Thea fights and kills her father, Malcolm Merlyn.
- This episode title card goes through several arrowhead designs from past seasons, from the first to the newest, as a reference to being an anniversary episode.
- After being rescued by the Waverider, Thea states, "This is exactly twice as many spaceships as I ever thought I'd be on!" Even though she referenced being on zero, she was on two spaceships, which is infinitely many more times than she imagined.
- Laurel's canary necklace in the dream world has the Black Canary's logo from the Birds of Prey in the comics.
- Oliver waking up in a world where he isn't Green Arrow is similar to episodes of , , & Batman: The Animated Series.
- In the episode, "", the Black Mercy causes Kara to wake up in a dream world where Krypton never blew up, and she never came to Earth and became Supergirl. Diggle even brings to Oliver's attention that he has "everything" in the dream world. This itself is a nod to the story "For the Man Who Has Everything", which was adapted as an episode of Justice League Unlimited.
- In episode, "", Barry lives in an alternate timeline he created where he stopped The Reverse Flash from killing his mother and despite having his speed, doesn't need to be The Flash.
- In the Batman: The Animated Series episode "Perchance To Dream", Bruce Wayne wakes up in a world where he is not Batman, his parents are alive and he is engaged to Selina Kyle.
- During the scene where Laurel is getting dressed for her wedding, her hands inconsistently switch positions between shots.
Preparation ran from September 14 until September 22, 2016. Shooting ran from September 23 until October 7, 2016.
- ↑ Arrow Episode 100 “Invasion!” Description: Katie Cassidy’s Role Confirmed - GreenArrowTV
- ↑ 
- ↑ Colin Donnell (@colindonnell) - Twitter
- ↑ Colin Donnell (@colindonnell) - Twitter
- ↑ Marc Guggenheim (@mguggenheim) - Twitter
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