With four hit DC superhero shows on the air, it was only a matter of time before The CW brought them all together for a massive crossover event. Last week we got the first such crossover, as Supergirl, The Flash, Arrow and Legends Of Tomorrow all combined for what the network dubbed “Heroes Vs. Aliens”, a four-night event that gathered all of the network’s superheroes together in a loose adaptation of the DC Comics Invasion! saga.

Crossovers have always been popular on television, and it’s well established that comic book fans love to see their favorite heroes interact with each other. All week long, fans followed the story from one series to the next as the alien force known as the Dominators threatened the Earth, setting the stage for the biggest superhero team-up ever seen on television.

With four great shows merging together for one week, viewers were treated to a number of memorable moments that will only intensify their desire for another big crossover event next season. Here are the Best Moments"Heroes Vs. Aliens" Had To Offer.

15. Little Things

Before we get into the big stuff, it should be noted that with a number of our favorite characters interacting for the first time, there were a ton of memorable little moments throughout the course of this crossover. Diggle’s deadpan reaction to Supergirl’s display of her powers was perfect, as was Heatwave’s odd chemistry with Kara (talk about an unlikely pairing).

It was also great from both a character and logistical standpoint to see Cisco gift Kara with a device that will allow her to cross between dimensions at will, which should facilitate more crossover events like this.

It was also intriguing to see Professor Stein learn that he had caused a time paradox which created a daughter he had never previously had. Struggling with that knowledge and ultimately deciding to risk damage to the timeline in order to preserve the existence of this new daughter gave Victor Garber a chance to flex his considerable dramatic muscles, and it will be interesting to see what ultimately becomes of this new character.

14. Barry, Cisco and Supergirl

While officially a four-night crossover, Supergirl’s contribution to the event was admittedly a little lacking. Monday’s episode, ‘Medusa’, served as the its mid-season finale, so it was charged with wrapping up as many plotlines as it could while setting the stage for new episodes to come next year. As a result, the crossover material was minimal. After Kara and friends had dealt with the threat of Cadmus, she returned home just in time to see Barry and Cisco arrive from their Earth to enlist her help.

The great chemistry between Grant Gustin’s Barry and Melissa Benoist’s Kara had already been established in last year’s “World’s Finest” episode of Supergirl, and they picked up right where they left off. Adding Carlos Valdes/Cisco into the mix just added to the charm, even though he and Barry are currently at odds. It’s a short scene of Barry and Cisco dropping in to Supergirl’s apartment, but it sets the stage for the fun interplay between characters we don’t usually get to see interact.

13. “Aliens!”

When Team Flash are alerted that a meteorite is approaching Central City, it seems like just another day at S.T.A.R. Labs, until Barry races out and finds it’s something else entirely.

The ‘Invasion’ begins with the crash landing of a Dominator ship. Barry’s reaction to discovering the ship is perfect; his astonished, “Guys, this isn’t a meteor” showing that even with everything he has seen (and done) since becoming The Flash, the arrival of aliens is still a shock of immense magnitude. Gustin’s performance is even better when Barry approaches the ship and is confronted by a veritable stampede of Dominators rushing off the ship. Between the eerie music and Barry’s shocked expression when he utters the obligatory and wonderfully cheesy “Aliens!!!”, it’s a great start to the titular “Invasion!”

It’s worth noting that the Dominators look pretty good too, considering the TV budget the shows work with. Even if a few extra dollars were funneled in to these crossover episodes, they still did more with less than a lot of movies manage to.

12. Dominator History

Of course aliens have been here before, and of course the government covered it up. That’s a staple of every invasion story worth its salt!

When Team Flash assembles after Barry’s discovery, Argus chief Lyla Michaels arrives to debrief them. It turns out the Dominators first arrived on Earth in 1951, killed and kidnapped American soldiers, and promptly disappeared. The assumption is that they were studying humanity’s weaknesses, but the expected invasion never followed. Lyla also reveals that the Dominators sent a message of warning three months prior to their latest arrival, signalling their intentions to once again study humanity and warning against any attacks.

With this backstory, the Dominators are established as more than just a mindless invasion force bent on death and destruction. Their transmission of a warning well in advance of their impending arrival is interesting, and could be interpreted as a genuine attempt at peace, or at least a desire to meet humanity on even terms.

11. Meeting Supergirl

The ability to include Supergirl after her show’s move to The CW was one of the best reasons to do this crossover event in the first place. Having already seen her alongside The Flash last year, The CW’s superhero fans were eager to see how she would play off other characters.

Melissa Benoist’s easy charm as Kara immediately lightens the mood, no matter how serious of a matter an alien invasion is. When Barry promises to bring a powerful alien to the team and arrives with an unassuming young woman (wearing a cape, granted), it’s a surprise to the hardened warriors in the room. Of course, all it takes is for Kara to hover in the air and carve her symbol in the ground with her heat vision to prove she’s everything Barry promised and more.

Sparring with Supergirl as a means to prepare for battling aliens is a clever idea on Oliver’s part, and gives us an excuse to enjoy some friendly battle between our favorite characters, though it’s never much of a battle. Even the combined might of heroes like Green Arrow, Firestorm and The Atom isn’t much compared to a Kryptonian on Earth.

10. Pep talk

As the first two superheroes to stake their claim in The CW’s DC universe, Oliver Queen’s Green Arrow and Barry Allen’s Flash have always had a unique relationship. Stephen Amell has excelled in his role as the (comparatively) grizzled veteran who has plenty to teach Grant Gustin’s Barry about the hero business, super speed or no.

Like any good superhero friendship, the pair have found themselves at odds at times, and Barry’s constant hope and optimism is a marked departure from Oliver’s more grim approach. Yet, the two understand each other better than any of their respective friends possibly can.

In that spirit, it was fun (and fitting) to have Oliver be the one to drag Barry out of his Flashpoint spiral of guilt. There’s no doubt that Barry made a selfish decision when he chose to go back in time and save his mother from Reverse Flash, but as Oliver points out, he would have done the same thing to save his own parents if he had possessed Barry’s power.

9. Heroes vs. Heroes

You can’t have a superhero crossover without a giant superhero battle. Somehow, when superheroes come together, there is bound to be some kind of misunderstanding that results in at least a few pages (or in this case, scenes) of costumed mayhem. It may be a cliche, but it’s a good one.

In this case, it’s the Dominators luring a number of the heroes into a trap and using a mind control device on them that sets the stage for a massive hero vs. hero battle. Supergirl, Firestorm, John Diggle, Thea Queen, Heatwave, White Canary and The Atom all get bent to the Dominators will, and they return and attack Green Arrow and The Flash. It’s an incredibly lopsided battle, even with Barry’s remarkable speed.

There are a number of highlights in the ensuing battle, from Oliver and Barry bickering about the situation and almost getting perforated by heat vision to Flash and Supergirl going on a high-stakes race through the city.

8. Perfect Life

Arrow’s Invasion episode also happens to be its 100th, a huge milestone for any show. So in addition to acting as the third of four parts of the crossover, the episode had to serve as a satisfactory ‘celebration’ of Arrow’s run up to this point.

They managed that by having the Dominators abduct Oliver, Thea, Diggle, Ray Palmer and Sara Lance, and place them in a shared delusion of a different life, allowing for a number of departed characters (friend, enemy and family alike) to return and play a part in the episode. And really, you can’t do an alien invasion without somebody getting abducted!

The ‘perfect life’ scenario is different for all of the captives, but Oliver’s domestic bliss with the late Laurel Lance is particularly effective. It’s a world where Oliver never became the Green Arrow, but John Diggle did. Thea is a confident young woman, Sara never became an assassin and Ray Palmer is engaged to Felicity. Everyone is happy, but something is missing.

7. Fighting the Dream

Each captive is initially at home in the delusion that the Dominators have stuck them in, but as they interact with each other, they become haunted by flashes of their real lives. As happy as Oliver is to be engaged to Laurel and have his parents with him, it doesn’t feel right. Neither does Ray’s life with Felicity, or Sara’s carefree existence.

When they decide to leave (though Thea is initially, and understandably, content to stay with her parents, even if they’re not real), the dream world fights back with appearances from old enemies like Damien Darhk, Deathstroke and Malcolm Merlyn. It’s unfortunate that more old enemies couldn’t return, like Ra’s Al Ghul (or Manu Bennett under Deathstroke’s mask) but that probably came down to scheduling.

It’s an old story, a hero having to choose to abandon a perfect but false reality in order to return to the imperfect real one, but it’s effectively told here.

6. Metahuman Studies

Why go to the bother of abducting five of Earth’s heroes, and why specifically the plain old powerless human ones? That’s the question faced by the group after they escape from the dream and are saved by the Legends and their Waverider ship.

Ray, smart guy that he is, posits that they were being studied for the knowledge they possess of Earth’s metahumans, and he’s not far off the mark.

When Cisco and Felicity join the Legends in their trip to the past and the first invasion of the Dominators, they learn more about the aliens and their purpose (and the government’s role in the conflict). The (then recent) rise of the Justice Society of America alerted the Dominators to the presence of these ‘metahumans’, and they wanted to assess the potential threat. Over fifty years later, with even more metahumans on the scene, they return.

With so many science fiction stories focused on aliens that feel threatened by Earth and its inhabitants, it’s clever and fitting that the Dominators be motivated by a similar concern about superheroes.

5. Breaking the Truce

The shady government operative (who happens to be present in both 1951 and the present day) is the one to inform the assembled superheroes that Earth had a truce with the Dominators after their previous visit, and that the truce has been broken by Barry’s actions in creating the Flashpoint timeline. It seems the aliens can’t abide the existence of a metahuman powerful enough to completely rewrite history itself, even if it is (presumably) just Earth’s history.

It’s another reason for Barry to feel guilty about what he did, even as he was just starting to feel better about it after Oliver’s speech. As if changing the lives of his closest friends wasn’t enough, he now has potential worldwide destruction on his conscience.

The aliens demand Barry be surrendered to them, or they will drop a bomb capable of killing all metahumans, not to mention millions of regular people. That raises the stakes about as high as they can go.

4. Changing the Past

Jumping back to 1951 to capture an alien and learn their plans sounds like a good idea, but naturally it goes wrong. The Legends and their new alien friend are promptly captured by the government, inspiring Felicity and Cisco to grab some future tech and mount a rescue mission.

Now, for two seasons the Legends have been learning how important it is not to mess with the past (though it’s a lesson that still hasn’t completely sunk in). Cisco has spent the better part of the season blaming Barry’s Flashpoint escapades for the death of his brother. But when given an opportunity to do some good in the past, he can’t resist the opportunity, and convinces the team to save the captive alien from the government’s grasp. Returning to the present, however, they learn that that same alien is at the vanguard of the invasion. With the entire planet at risk, Cisco learns first hand how a choice made with the best of intentions can create terrible consequences. That gives him some much needed perspective on Barry’s own choices, and finally puts the pair on the road to reconciliation.

3. “You and what army?”

Barry, being the hero that he is (poor choices not withstanding), doesn’t need to think twice when he learns the Dominators want him in exchange for halting their attack on the planet. He fearlessly prepares to hand himself over to the aliens and suffer whatever terrible fate they have in mind for him.

Luckily for Barry, his friends are heroes too. In one of the best moments of the entire crossover event, Oliver tells Barry he won’t let him turn himself over. Barry responds, “no offense Oliver, but you and what army?” only to turn around and find an entire array of superheroes standing in front of him.

It’s a ‘jump up and cheer’ moment, not just for the clever wordplay, but for finally bringing everyone onto the same page. Oliver and Supergirl have never wavered in their support for Barry, but for everyone else it’s a chance to overcome their anger at his timeline meddling and unite under a common purpose. Most importantly, with Cisco having gained some perspective on just how seductive changing the past can be, he steps forward and offers Barry his friendship again.

 2. War of the Worlds

Finally, at the end of four (okay, mostly three) interconnected episodes, we get the alien smackdown we were promised, and it doesn’t disappoint. With the Dominators invading (and dropping their meta-human bomb), the combined forces of Supergirl, Team Arrow, Team Flash and the Legends of Tomorrow come together to protect Earth. The ensuing fight scenes are great not just for the impressive choreography and special effects (for TV anyway), but for pairing off characters who almost never interact. There were a ton of cool little moments, from Green Arrow and Heatwave working in tandem and Atom saving Diggle from a rampaging alien to Supergirl swooping in and catching a falling Oliver.

The secondary element of the battle is Flash and Supergirl racing around the country slapping nano-weapons on every alien, while Firestorm manages to transmutate the meta-human bomb into harmless liquid. When the Dominators fall back, signalling the end of their invasion, it’s a hard fought and well earned victory.

1. Drinks

Oliver and Barry are the two that started it all, so it’s only fitting the crossover end with them sharing a drink and bonding over yet another close call. Thanks to the Flashpoint timeline and the Dominators manipulations, both Barry and Oliver have now been able to take a long look at what their lives might have been like had they never started down the path to heroism. In both cases, they were happy in their normal lives, but they knew something was missing. Ultimately, in true heroic fashion, and in spite of all of the sacrifices they’ve had to make, they realize they made the right choice, even if their lives will never be normal.

On a show about superheroes, you wouldn’t think a quiet moment between friends in a bar would be all that memorable, but it’s a testament to the characters Stephen Amell and Grant Gustin (and the writers) have crafted that it’s rewarding just watching the pair share a drink at the end of a long day.

There were no shortage of memorable moments in the four-night “Heroes Vs. Aliens” crossover. What were some of yours? Let us know in the comments.