If you would have through an obscure show like Arrow would one day blossom to have their own coherent small screen universe (that many think is better than DC’s big-screen counterpart), way back in 2012, you might have been called crazy at the time.  Now, though, this is the “age of superheroes” in our pop culture.  You can’t help but blink and there will be a superhero film or TV show somewhere within mass media.  The Arrowverse has been very successful on the CW as a result of literally bringing a comic book to life through shows like Arrow, The Flash, Legends of Tomorrow, and Supergirl.  With each show under the CW’s umbrella, that leads to the possibility of a crossover.

Each year the crossover potential has continued to grow.  The first try was when they introduced Barry Allen (The Flash) on Arrow, which led to his Barry getting his own spinoff show and expanding the Arrowverse.  The second time was “The Flash vs Arrow.”  The third time, the “Heroes Join Forces” even helped create the Legends of Tomorrow to create their own show.  Last year’s “Invasion” crossover was a success as heroes from all four shows combined together to save the earth from the alien race of The Dominators.  That crossover even was so successful, it’s a no-brainer that they would do another one.  This year the powers that be decided to have the crossover be over 2 nights instead of four, combining the event on back to back (Supergirl/Arrow and The Flash/Legends of Tomorrow) shows during that time.  The event consisted of the heroes uniting against the foes of Earth-X on “Crisis of Earth-X.”

We know that there are countless versions of Earth within the DC Multiverse.  Within the Arrowverse, there are 52 different Earth (paying homage to DC’s “New 52”).  Most of the earths we have seen so far are similar to the ones that already exist.  Some things are a little different, but not too different.  However, this week, we are introduced to a brand new earth, Earth-X, which is unlike any we have seen so far.  In this reality, the Nazi’s won World War II and rule the planet with an iron fist.  Because this earth is within the Arrowverse, we see doppelgangers of people we know.  For example, the “Führer” is none other than the “Dark Archer” Oliver Queen, who rules the Nazi-occupied planet after Hitler’s death.  He easily dispatches resistance fighters led by Supergirl’s James Olsen/Guardian.

Meanwhile, on Earth-1, everyone’s getting ready for the wedding of the century.  All season Barry and Iris have been slowly moving towards their big day, and now it’s upon us.  We see a brief montage of all the characters as they are dealing with bad guys, but also forgetting to plan or RSVP for the wedding.  Barry is fighting King Shark (ARGUS prisons are just as bad as Arkham Asylum) while discussing last minute plans with Iris in Central City.  Oliver is fighting ninjas in Star City while talking to Felicity about the wedding.  The Legends are fighting in 1183 England while forgetting to RSVP.  Supergirl is in Earth-38 fighting a Dominator who is “so last year” when she invites her sister Alex to be her plus one for Barry’s wedding.  We get it, you superheroes are too busy to RSVP, but you still need to!

As everyone arrives to get ready for the wedding, a thousand mini-stories are going on at once.  Both Oliver and Felicity talk about the possibility of the two of them getting married while they talk within their own circles (this plays a big, frustrating role later).  Stein and Jax continue their discussions about breaking up Firestorm so Stein can leave the Legends and be with his family.  While Caitlin and Cisco have developed a magical serum which will do it, Jax doesn’t seem too pleased about their upcoming breakup.

At the rehearsal dinner, a few interesting things happen.  Alex, fresh off her breakup with Maggie talks with Sara, which we all know what’s gonna happen next.  After a few shots, the two of them quietly leave the dinner while smooching all over outside of Jitters.  After Joe delivers a toast to his two children and his love and happiness for the both of them, Oliver gets the brave idea of proposing to Felicity.  It did not go as planned.  Felicity is not interested in “a piece of paper” and as the two quietly argue about the idea of marriage Felicity screams out “I DON’T WANT TO MARRY YOU!” for everyone else to hear.

The next day is the big event.  Everyone arrives at the church.  Barry, like any groom, is nervous.  He is offered a refreshment by one of the ushers.  She seems just a little too excited to be at the wedding for a normal usher.  The usher is played by actress Jessica Parker Kennedy (Black Sails, Colony), who looks like a perfect blend of Barry and Iris in real life.  Her looks and the fact that the character is too excited for the wedding to lead me to think that she’s Barry’s daughter from the future: Dawn Allen, one of the “Tornado Twins” from the comics.

The ceremony begins with Kara singing a great rendition of “Run to You,” reminding us that Barry sang that to Iris during last year’s musical crossover on The Flash/Supergirl crossover “Duet” and that actress Melissa Benoist can carry a tune.  As the vows are ready to be exchanged the priest ask anyone to speak now, or forever hold their peace, and he immediately gets vaporized by heat ray vision.  In comes the Nazis from Earth-X.  With so many heroes in one place, they spring into action.  Oliver just happened to have a bow and arrow to bring to a wedding.  Caitlin turns to Killer Frost.  Even Wally helps.  Supergirl faces off against her Earth-X counterpart.  Oliver faces off against his.  Alex and Sara team up and face off against Earth-X’s version of Prometheus.  Kara manages to defeat her counterpart and Oliver’s retreats.  They manage to take X-Prometheus into custody at Star Labs.  Thanks to the Legends memory wiping device, no one knows all their secret identities.  Rory says it best, “Best Wedding Ever” as he enjoys a celebratory snack.  Later on, the Earth-X villains regroup and take off their masks, revealing that Oliver, Kara, and Harrison Wells/Eobard Thawne are the Earth-X bad guys.

As they unmask “Prometheus,” he’s revealed to be none other than Earth-X’s Tommy Merlyn, Oliver’s best friend and Thea’s half-brother who died way back in season 1 of Arrow.  Oliver is a little blindsided and tries to speak to this Tommy as though he’s his old friend.  That quickly stops as he tells Oliver that this version is weak compared to the Führer, and he quickly takes a cyanide pill to kill himself.  While it was nice to have actor Colin Donnell back, this was the briefest of brief cameos and didn’t serve much of a point.   But it was at least better than the CGI Tommy from last year’s crossover episode.

Of course, there’s more Oliver and Felicity drama.  Just when you think the two of them are done making unnecessary self-inflicting drama against each other, they tell you to “hold their beer.”  After everything dies down, Oliver tries to talk with Felicity about wanting to be married.  She tells him that they have a “great” thing and she doesn’t want to mess it up.  That’s kinds the same impasse that Alex and Maggie had concerning to want to have children that can forever ruin a relationship.  Later on, she reveals to Iris that her reasoning is because the last time they were going to get married, she got shot.  An explanation, but a dumb one.

Meanwhile, Stein reveals to Jax a formula he made that will give him superpowers after they separate from each other as Firestorm.  The powers will give him the ability to be adhesive towards surfaces, basically Spiderman without the strength and webbing.  Jax still isn’t pleased.  As he and Stein talk, Jax reveals to him that the separation of Firestorm is the separation of their relationship.  He doesn’t care if he doesn’t have superpowers, he wants his adoptive father figure, who will be leaving him forever.

The team thinks that they know where the Earth-X folks will be and launch a surprise attack.  Oliver, Kara, and Barry meet up with Reverse Flash and X-Supergirl.  Meanwhile, X-Oliver has gone to STAR Labs.  There, he takes on Rory and Caitlin as well as all of Team Arrow (who finally showed up just to get beat down).  During the rest of the heroes to the docks, the Earth-X folks take down the rest of them as they have their own version of Metallo.  They take all the heroes and put on collars to block their powers, except Kara as they need to take her heart out and give it to the X-Kara.

Barry, Oliver, Alex, Stein, Sara, and Jax wake up in a Nazi prison camp on Earth-X, complete with “star” prisoner uniforms as well for other people on Earth-X.  One prisoner Ray Terrill (guest starring Russell Tovey) is imprisoned for being gay and not fitting the Nazi’s Aryan ideals.  One of the Nazi commanders is the Earth-X version of Quentin Lance who recognizes Sara as looking similar to his own daughter, who he killed for being bisexual.  As he’s getting ready to execute them by firing squad, in comes Captain Cold!  Wentworth Miller returns for his CW role, even though the Earth-1 Captain Cold died in the first season of Legends of Tomorrow (and thanks to the time-traveling nature of the show, managed to guest star a few times), but his Earth-X counterpart is part of the resistance.  After he removes Ray’s collar, it’s revealed he’s a metahuman as well, who can fly and blast energy, very Firestorm-esque.  Ray reveals that he is from Earth-1 originally, but he also is Captain Cold’s boyfriend in this universe.  Wentworth Miller in real life is gay and finally got to play a character as such in the Arrowverse.

Afterward, the team head to the resistance headquarters at Earth-X’s STAR Labs led by the Earth-X version of Winn, General Schott.  This version of Winn is not as nice and easy-going as he is on Earth-38.  This one is hardened by generational war.  They realize that the only way back to Earth-1 is through a gateway at a Nazi facility, however, Winn wants to destroy it.  Even after pleads from Alex, he won’t budge.  Captain Cold (“Leo” in this universe) pleads with his superior, who allows them a one hour head start) before sending Earth-X’s version of Red Tornado to destroy the facility.

With it being a heavily armed facility, there’s no way the heroes could take it head on.  Lucky for them, Oliver happens to have the same face as the leader of the Nazi party.  Captain Cold donning a uniform escorts Oliver through the gate.  Everyone else waits for him to turn down the power dampening field.  Oliver is found out soon enough by Quinten Lance who requests he shoot the Earth-X version of Felicity and he can’t bring himself to do it.  He does, however, overpower just about all the Nazi’s in the control room, allowing the rest of the heroes to enter and fight their way through.

Back on Earth-1, Eobard Thawne is preparing Kara’s surgery by saturating her with red solar radiation.  All the other heroes have been rounded up and placed into metahuman cells, except Felicity and Iris, who sneak around unnoticed.  Felicity writes a computer program to turn off the power just as the surgery is about to start.  Eobard tried to find them but Metallo beats him to it.  Felicity stands her ground in not revealing the codes.  Thawne tells her that he’s from the future, and there’s no record of her, so he has no problem with killing her as his hands vibrate.  Kara tells her to give the code as she will not be responsible for Felicity’s death.  The power’s then restored.

On Earth-X, as the heroes are trying to storm the facility, X-Winn decided he’s given them enough time and launches Red Tornado to take the building down.  Barry and Ray try to fight the unstoppable robot while everyone else is fighting Nazis.  Jax and Stein needed to separate as Firestorm to turn on the portal.  Unfortunately, that’s when the Nazis start shooting all over the place.  Stein tries to pull the lever but gets shot in the back.

Now it’s no secret that actor Victor Garber was leaving the DC CW to act on Broadway (hence the reason for separating Firestorm), but for him to get shot was still tough, especially with all the talk about going back to his family.  He manages to pull the lever and get shot again.  Jax then has the two of them merge as Firestorm to help heal them with the hope that he can be repaired on The Wave Rider.  All the heroes escape through the portal and head back to Earth-1.

Back on Earth-1, Kara is back under the knife, getting ready to get her heart taken out.  Just as Thawne is about to stick the knife into her, he can’t push any further.  Zoom in and we see Ray Palmer in Atom form holding back the knife.  The rest of the Legends have arrived to help save the day.  They destroy Metallo and everything seems OK.  Unfortunately, X-Oliver is holding Felicity hostage, leading Oliver to do the same with X-Kara, X-Oliver’s wife.  Thawne speeds in and removes the two of them out of the equation.

On the Wave Rider, Caitlin is tending to Stein.  However, Jax starts coughing up blood as well.  Because of their Firestorm connection, Jax is the only thing keeping Stein alive.  The longer he tries, the more he is likely to die as a result.  Caitlin doesn’t have the heart to tell Jax, but knows this won’t end well.  Stein realizes this and tells Jax that he will have to die to save the two of them.  He tells Jax that he loves him like a son.  He takes the serum to separate the two of them and dies peacefully next to a tearful Jax.  This causes all the heroes to feel sorry for him.  It hits many of the Legends in different ways, but really hits home for Sara (the team leader) and Jax of course.

But we still have some Nazi to deal with.  X-Kara is starting to succumb to her radiation and will explode, taking all of Earth-1 along with her.  She threatens the planet under the condition that Kara goes with her.  Oliver, who last year didn’t like Kara tells X-Kara that he won’t abandon her.  They then take the fight to the Nazis.  During the battle, everyone gets a chance to shine as we get another heroes montage as they fight their Earth-X counterparts.  The battle ends with X-Kara going supernova and Kara taking her into the stratosphere to stop the planet from exploding.  X-Oliver devastated tries to kill Oliver, who strikes him with an arrow through the chest.  Barry doesn’t bring himself to kill Thawne who he lets go, promising to return once again, with a different face.

Jax goes to Stein’s home to tell his wife and daughter the terrible news as they all have a group hug.  Jax delivers a eulogy for him.  Each member has something to say to the departed Stein, even Rory has “allergies.”  Kara and Alex head back to Earth-38.

However, Barry and Iris still have a wedding they want.  Instead of something extravagant, they just want it done quick and easy.  Oliver knows someone who’s ordained: Diggle (who was missing all this week), and Barry speeds him back to them.  After throwing up (as he hates being zipped everywhere by Barry), Diggle agrees to perform a marriage for Barry and Iris.  Just before he can start the “ceremony,” Felicity decides that she is also ready to take the plunge with Oliver and asks Diggle to marry the two of them as well.