Crisis on Earth-X, Part 4

"Crisis on Earth-X, Part 4" is the eighth episode of the third season of DC's Legends of Tomorrow, and the forty-first episode overall. It aired on November 28, 2017. The episode is the final part of a four-part crossover with the eighth episode of the third season of Supergirl, eighth episode of the sixth season of Arrow and eighth episode of the fourth season of The Flash.

Synopsis
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.

Plot
Kara is saved from Thawne by Ray Palmer, while Nate releases everyone from the pipeline.

On Earth-X, Stein activates the portal before succumbing to his injuries. Jax bonds with Stein to get him through the portal and back home, along with Barry, Oliver, Sara, Alex, Ray Terrill and Leonard Snart.

Members of all the teams face off against Earth-X Metallo, while Felicity and Kara are cornered by Dark Arrow. Oliver gets Dark Arrow into a stalemate by threatening to kill Overgirl. Stein is kept alive by his connection to Jax, but it is slowly killing them both.

Stein severs their connection after an emotional conversation with his "Son" Jax, thanking him for the greatest adventure ever.

Stein asks Jax to stay with him and a few minutes later dies from his injuries; the loss of Stein give the team the drive to continue the fight and to stop the Earth X invaders.

Jax delivers the news to Clarissa and Lily that Stein has died saving his friends.

Dark Arrow contacts the team to offer a truce, saying they will leave in peace if the team surrenders Supergirl. Oliver refuses and the team battles Nazis and the Earth-X doppelgängers, with Cisco, Wells, Felicity and Iris piloting the Waverider.

Caitlin, Amaya and Zari infiltrate the Nazi's timeship Wellenreiter to disable its shield before Harry destroys it. Defeating Thawne, Barry is unwilling to kill him, allowing him to escape.

Supergirl battles Overgirl, with the latter eventually going nuclear. Kara flies her into space, where she detonates. Oliver subsequently kills his doppelgänger. Cisco opens a breach, allowing Ray to return to Earth-X, with Snart choosing to stay.

The team holds a funeral for Martin, where they all pay their respects and Jax wonders what is next for him, now that Stein is gone.

The Legends, Kara, and Alex depart back to their own lives. Barry and Iris get Diggle to ordain their vows and officially marry, with Oliver and Felicity doing the same.

Trivia

 * Dinah likens Metallo to the Terminator from the Terminator franchise.
 * Cisco compares flying the Waverider to playing Star Raiders on the Atari.
 * When Supergirl says to Overgirl "General, do you care to step outside?", it is a reference to Superman II when Superman says the same thing to Zod.
 * Asked by Cisco if he can handle piloting the Waverider, Harry quips that it's a "walk in the park, Kazansky", quoting the 1986 film Top Gun
 * When Overgirl begins to go nuclear, Harry tells Supergirl that she has to fly her "Up. Up. And away", referencing the infamous Superman catchphrase "up, up, and away".
 * When Kara asked Felicity and Ray how they know each other, they said that they used to date, referring to the events of the third season of Arrow.
 * The picture that Ray was looking at after Martin's death is from the episode "The Magnificent Eight".
 * When Steel catches Supergirl, it is an homage to the cover of Crisis on Infinite Earths #7, in which Superman holds Supergirl (Nate even making a reference to himself being a "man of steel").
 * Former Arrow actress Susanna Thompson has an uncredited role as the voice of the the A.I. of the Wellenreiter.
 * Harry Wells says "Cut the chatter, Red Two", a reference to Star Wars: Episode IV A New Hope.
 * Ray says "Mitts off Mengele". Referencing Dr. Josef Mengele.
 * Earth-X's Snart makes an overture towards Sara, a callback to their implied relationship in Season 1, thereby also suggesting that he, like Sara, is bisexual.
 * This episode features the last appearance of present day Martin Stein, following the events of this episode.
 * When Harry is imprisoned along with Cisco he annoyingly throws a ball against the wall of his cell, this could be a nod to The Great Escape where Steve McQueen's character does likewise.