Spoiler warning: Do not read on unless you’ve seen the “Arrow” installment of The CW’s superhero crossover event, titled “Legends of Yesterday.”

In the second part of The CW’s two-night “Arrow” and “The Flash” crossover event, Oliver (Stephen Amell) and Barry (Grant Gustin) took on Vandal Savage (Casper Crump) for a second time, in an attempt to stop the immortal villain from killing Hawkman (Falk Hentschel) and Hawkgirl (Ciara Renee).

The heroes faced off with Vandal early on in the episode with disastrous results. With Oliver distracted by the discovery that he has a son and his ensuing fight with Felicity (Emily Bett Rickards) once she found out that he’d tried to hide the truth from her, the heroes went into battle under-prepared, allowing Vandal to get the upper hand and kill everyone except Barry, before destroying Central City with the Staff of Horus. Thankfully (for the future of both shows), Barry managed to run fast enough to travel back in time and warn Oliver of their fates, enabling them to undo many of the mistakes they made in their previous confrontation with Vandal, eventually obliterating him. Oliver also got to spend some quality time with his son, William, while the Hawks prepared to go off and get to know each other better in the lead up to “DC’s Legends of Tomorrow.”

As for what happens next, the executive producers of all three shows weighed in on the “serious consequences” that will result from Barry and Oliver’s actions in Wednesday’s episode.

Sins of the father

In both versions of the timeline, Oliver chose to keep his son’s existence a secret from Felicity – the only difference is that the second time around, Felicity didn’t inadvertently find out the truth from Barry. But it’s only a matter of time before Oliver’s decision rears its head again, according to “Arrow” executive producer Wendy Mericle.

“It’s definitely going to come to a head in the middle of the season. We can’t tell you how that’s gonna happen. But obviously for the arc of Oliver and Felicity’s relationship this season, the fact that he’s keeping this from her … true to what we’ve done on the show, if there’s a secret somewhere, it’s going to come out and it’s going to have some serious consequences,” she noted. “We’re really excited about how that’s going to change things and it’s really gonna raise the stakes and throw some wrenches into the works of their relationship — which so far this season has been pretty smooth sailing. True to form, we’re gonna really mine that. There’ll be some fallout for both of them.”

Comic book fans of Green Arrow might’ve been surprised to hear that Oliver’s son was named William Clayton, and not Connor Hawke, as many had been expecting, but exec producer Andrew Kreisberg explained that the choice was made in order to keep the door open for Connor somewhere down the line, rather than closing it.

“When we came up with the whole idea of it, part of it was we didn’t want to be tied in to a character like Connor not being able to be part of the show if we made him so young,” he explained. “So to give us the leeway to still have Connor Hawke be part of the universe without [being too young], that was the biggest reason we made that decision. It’s actually one of things I think all of us are most proud of and, again, having the kind of partners that we have that we’re able to basically have one scene in one episode in season two, knowing that we were eventually going to get to this point and that it is all set up and all tied in to Oliver’s mother… And Susanna [Thompson] hasn’t been with the show for a while now, and yet her presence is still felt all throughout this story. There are some things that happen when you do a show for a long time that are just happy accidents and then there are other things that you plan on and this is one that we really planned on.”

Be kind, rewind

Barry’s last couple of experiences with time travel have had grave repercussions — especially when Barry has changed the past to avert a death. The producers played coy on what the fallout might be from Barry’s do-over with Vandal Savage, with Marc Guggenheim teasing, “I think you’re gonna have to watch upcoming episodes of ‘Arrow.'”

Ashes to ashes

Because of Barry’s trip back to the past, he and Oliver succeeded in incinerating Vandal Savage, but we already know that the immortal bad guy will be the primary antagonist in “DC’s Legends of Tomorrow,” and apparently Malcolm Merlyn (John Barrowman) has a part to play in the villain’s unlikely revival, judging by the way the new Ra’s al Ghul gathered up what was left of him. Don’t expect to see much explanation for that on “Arrow” or “The Flash,” though, per executive producer Greg Berlanti.

“As of right now, we’ve almost always saved it for ‘Legends.’ But we’re not done with the seasons on those two shows yet so I don’t want to say we wouldn’t come up with some kind of way to reference it,” he said.

On a related note, Berlanti confirmed that aside from this week’s crossover, “once ‘Legends’ is born in January, there’s really no intersection [with it] on the other shows. ‘Legends’ is kind of its own wacky, crazy kind of thing that allows for some fun surprises in terms of who may visit and how because they’re flying through the timeline and you’ll start to see more of that. But not on ‘Arrow’ or ‘Flash.'”

That means past versions of our existing heroes and future versions could make appearances, although Guggenheim declined to give specifics, noting, “part of the fun of ‘Legends’ is the fact that it takes place all throughout history, future and past, so … one of the things we’re having so much fun with is that everything is up for grabs. Anything is possible.”

Good vibrations

Sadly, while the crossover allowed Kendra to discover her hidden history as Hawkgirl, it also prompted her to pump the breaks on her burgeoning relationship with Cisco (Carlos Valdes), who remains pretty unlucky in the dating department.

Luckily, Kreisberg promised that there are plenty of other developments to distract our tech wizard from his heartache in upcoming episodes.

“The two interesting things that are happening for Cisco are, one, a further exploration of his abilities as Vibe, and what he can do and what he’s capable of. The other thing — which you got a little bit of a glimpse of in episode 7 — is his relationship with new Wells [Tom Cavanagh],” he teased. “The Eobard Thawne version of Wells liked having a team, he liked having people around him, he liked cherry picking the best [parts] of other people and using their knowledge. And did it in a way that made them all feel good about themselves. And this Wells thinks everyone else besides him is an idiot … And like Cisco said, he’s a dick; he doesn’t make any apologies for that. And so much of that is coming from Tom’s talent and imagination. And his willingness to play someone who is kind of unpleasant.”

While we shouldn’t expect Wells to suddenly have a change of heart or, as Kreisberg said, “a kumbaya moment,” the EP did hint that “there are little chinks in his armor along the way, and watching that relationship with [Jay], and especially that relationship with Cisco and Barry as it moves forward — just as he’s seeing these people be selfless around each other … it is having an effect on him. That’s the big thing for Cisco.”

The producers said that Cavanagh has “great scenes” coming up with both Valdes and Gustin, and Kreisberg noted, “There’s a two-part episode, 13 and 14 this year, which I think is definitely the most fun pair of episodes that we’ve ever done, and has my favorite Cisco moment in the history of the series so far.”

Deathly serious

Between Barry’s time-travel do-over and Vandal Savage’s impending resurrection, you’d be forgiven for wondering whether death has lost its sting in the world of “Arrow” and “The Flash,” but the producers insisted that they’ve found ways to keep the stakes high.

“‘Legends’ will explain basically why time travel can’t be used in a deus ex machina kind of way, not just with respect to death, but with respect to any plot contrivance,” Guggenheim promised. “It’s like, ‘Why can’t we just go back to Episode X and do that episode differently?’ We’re going to answer that question very definitively. It’ll be part of the rules of time travel that are a part of ‘Legends.'”

Berlanti pointed out that in the comics, characters would die and stay dead for decades — “Barry Allen; he died for like 20 years,” DC Chief Creative Officer Geoff Johns noted.

Berlanti agreed, “Why that’s a perfect example is they all waited long enough, and Geoff chose to bring him back the right way. So dead will still mean dead, but it doesn’t always mean dead forever. Some characters it will, and some characters it won’t.”

He added, “We even say that sometimes when we sit down with actors to let them know their fate at the end of a season. We describe it to them, sometimes in this universe, if something comes to us that’s a really organic, cool way to bring a character back and is exciting to us and we feel like doesn’t devalue the death, but introduces them in another interesting way into the narrative, I do think that this genre that we’re making is different than other shows in that way.”

Mericle agreed, “[We try to] make sure it has – even if death is not always permanent – an emotional impact on the characters, regardless of whether we ever decide to bring them back, and on ‘Arrow,’ we can do that in the flashbacks, and obviously now that we have one universe, we can do it in all kinds of ways on the other shows. But for us, at least in terms of when we’re talking about the storylines on ‘Arrow,’ it always boils down to, ‘What kind of impact will this have on the characters? And is that something that is worth exploring?'”

The key to pulling off an effective death, according to Kreisberg, is “consequences. When Sara was brought back, when Thea was brought back, last year when Barry changed the timeline, this year when Barry changes the timeline, any of these things that feel like the right thing to do, there’s always a price to be paid, and whether or not that price gets paid immediately … or whether that price gets paid later on in ways that you don’t foresee, it always comes back to haunt you,” he noted. “We always talk about, on ‘Legends,’ Vandal is the Big Bad, but truly the Big Bad is time itself. Time wants to go in one direction, and I think that ethos… When people die, the universe wants them to stay dead. Anything you do to change that is going to have a cost. And that’s what these shows are, these characters constantly paying that price. For as much as these powers and abilities and technologies that they have, there’s always a price to be paid for using them.”

“The Flash” airs Tuesdays at 8 p.m., and “Arrow” airs Wednesdays at 8 p.m. on The CW.

What did you think of the “Flash”-“Arrow” crossover? Share your reactions and predictions below, and check out part one of our interview with the producers from the “Flash” installment