Spoilers below for the first part of the Arrow-verse's "Elseworlds" crossover.
After four seasons of seeing Barry Allen exclusively inside his ever-changing super-suits as The Flash, it was a refreshing hoot for the "Elseworlds" crossover to swap Barry and Oliver's identities. The two heroes had a pretty serious heart-to-heart at the Kent family farm, where Oliver told Barry where his no-nonsense intensity comes from. Iris certainly doesn't want to see her husband embodying the Green Arrow's dark side, but that negative energy might just come through a little more.
Late in the crossover's first part, Barry-as-Oliver dropped the familiar "you have failed this city!" quote to take out the robot Amazo. While it may have seemed like a fun easter egg for viewers, though, Iris took the tonal change in behavior to heart, pleading with Barry not to embrace Oliver's dark side. Here's what showrunner Todd Helbing said about it, according to EW.
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. 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. . . . There's an episode a little bit down the line where Barry deals a little bit with [Oliver's darkness seeping in].
What could that episode and/or moment consist of? Fans have only seen Barry Allen tapping into his dark side on rare occasions, with the future-sourced Savitar obviously coming across as (presumably) the most negative iteration of the speedster imaginable. It's highly doubtful we'll get anything quite as over-the-top as that, but it could be interesting to see Barry work some more of his issues out.
Todd Helbing did say that the upcoming episode would look into just how much of Oliver's dour pragmatism will be embodied within Barry, and I dare say that it won't be such a bad thing if Barry has a small pessimistic voice on one shoulder warning him against doing all of the impulsive things that he's already been trying to avoid doing in front of Nora. If anyone on this show could use a more balanced perspective, it's Barry, especially if Reverse-Flash is looming large for the rest of the season.
Which isn't to say that he should be a gloomy Gus throughout the rest of Season 5 and beyond. But now that Barry is a married dude with an adult offspring, which should always cause one to at least consider a new perspective, he might realize that treating the world as his sandbox isn't always the best play when helping those around him.
Barry's connection with Oliver was lauded as supremely important by Arrow star Stephen Amell, who said:
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.
On the flip side of Barry holding onto some of Oliver's more sour emotions, what about Stephen Amell's vigilante gaining a more all-encompassing sense of humor after spending so much time in Barry's shoes. It would below Felicity and Diggle's minds if Oliver returned to Star City dishing out quips and coming up with witty villain names. One can only hope.
With a big Gotham City introduction on the way, the Arrow-verse's "Elseworlds" crossover will continue with episodes of Arrow and Supergirl on The CW on Monday and Tuesday evenings at 8:00 p.m. ET. Stay tuned to see how they change each show up in the long run, and head to our fall TV schedule and our midseason premiere guide to tap into all the new and returning shows popping up soon.