The Flash boss teases how the 'Elseworlds' switcheroo affects Barry going forward

Warning: This post contains spoilers from The Flash‘s “Elseworlds, Part One,” which aired Sunday night. Read at your own risk!

Barry and Oliver’s Freaky Friday-like predicament in “Elseworlds” will have an effect on Barry later this season on The Flash.

In the first part of this year’s crossover, Barry (Grant Gustin) and Oliver (Stephen Amell) switched identities and powers and were forced to be the best versions of each other when they had to team-up with Supergirl (Melissa Benoist) and Superman (Tyler Hoechlin) to defeat Amazo, an android who can mimic metahuman powers. Oliver-as-the Flash had to use his speed to stop Amazo from phasing through the super-cousins’ steely grip so Barry-as-Green Arrow could fire an arrow that cook disable Amazo’s operating system. Embracing his inner Oliver Queen, Barry-as-Green Arrow promised to send Amazo straight to hell and said the iconic “you have failed this city” right as he fired off the winning shot.

In the moment, Barry’s dark turn seemed funny; however, it didn’t sit right with Iris (Candice Patton). After the fight, Iris pulled Barry aside and asked him to come back to her and to not actually become the darkness-consumed Oliver once the switch is reversed. He promised that he would and would always reveal his true face to her.

“I think it just speaks to everything they’ve experienced this year as parents for the first time, in that it really speaks to the relationship, how much they’re in love. ” The Flash showrunner Todd Helbing told reporters at a screening of the crossover. “I just think it really speaks to who they are as a couple and it sets up what they’re going to have to go through in the back half of our season.”

Helbing went on to say that The Flash will deal with whether or not too much of Oliver’s darkness seeped into Barry during the crossover. “There’s an episode a little bit down the line where Barry deals a little bit with that,” he said.

Before the climactic battle against Amazo, “Elseworlds, Part One” gave viewers an amazing callback to the first crossover. After jumping over to Earth-38 for Kara’s help, the two heroes used their time on the Kent Farm with Kara, Clark, and Lois Lane (Elizabeth Tulloch) to train, and Barry-as-Oliver fired two surprise arrows into Oliver-as-Barry’s back, which is essentially the reverse of what happened in “Flash vs. Arrow.” Although Barry was overjoyed that he finally got his revenge, Oliver was rather pissed because Barry was having such a good time with the Green Arrow powers, which led to a very earned heart-to-heart in which they discussed their different approaches to being superheroes. For Oliver to be the Green Arrow, he has to draw on his dark and painful memories, whereas Barry has to harness everything that makes him joyful to use his speed. This exchange was one of Amell’s favorite moments of the crossover.

“The fact that Grant and I have this exchange, and have this really cool moment sitting on the steps of the Smallville ranch, is pretty much surreal as it gets,” Amell told EW when we visited the “Elseworlds” set in October. “The most important relationship in this crossover is the relationship between Barry and Oliver, not just because of the theme of them swapping lives but just because I personally think that’s the most important overarching, macro relationship in the entire universe that we’ve made over the past seven or eight years. Some of the scenes they have are just very earned because of the stuff you’ve seen before in the crossovers but just done a little differently.”

The Kent-Farm set scenes also introduced both Tulloch’s Lois Lane and the iconic Clark-and-Lois relationship into the Arrowverse. “It was amazing to have Clark and Lois together on our show,” Supergirl co-showrunner Robert Rovner told reporters at the screening. “We’ve dreamed of having Lois Lane be on Supergirl. We’ve talked about her since the beginning, so that was great. When I first saw them together, it felt like we were kind of entering the canon in a new fresh way, seeing them kind of reunite for the first time in our universe, and that was thrilling. It was thrilling to really read their first scenes in Flash and to kind of feel Lois Lane. It was amazing, and Bitsie Tulloch is amazing, embodying kind of everything that is iconic about Lois and we just love them together.”

It doesn’t sound like there’s currently a plan to have Lois back on Supergirl, but Rovner did say he is open to it if the opportunity presented itself. “I think the plan was for her to be in this, but if DC lets us and the story takes us, we’d love to have her back,” said Rovner.

Looking ahead, the Arrow hour, which is part two of “Elseworlds,” sees Barry, Oliver, and Kara speed over to Gotham City to find Dr. John Deegan (Lost‘s Jeremy Davies), who is responsible for altering reality. Working with Davies was another highlight of the crossover for Amell.

As you already know, the Arrow hour will also introduce Ruby Rose as Batwoman, who isn’t too pleased when the Trinity shows up in her city.

“Elseworlds” continues on Monday at 8 p.m. ET with Arrow and concludes the following night at 8 p.m. ET with Supergirl on The CW.