It's an exciting time to be a fan of the CW's DC shows. With Supergirl moving from CBS to The CW, this opens up the possibility of frequent crossovers between the shows, and the giant four-show crossover planned for December this year is already shaping up to be pretty awesome.
But so far The CW has really pulled it off, deftly interweaving the narrative between Arrow and The Flash, setting up Legends of Tomorrow with another crossover episode. Now, everything's set to change because Barry's Flashpoint reset in The Flash finale will have consequences in every one of the CW's DC shows.
While Legends of Tomorrow is probably protected by all the time nonsense constantly going on in that delightful show, and Barry's affect on Arrow has been minimal, it's Supergirl that might actually be the most affected by these changes.
Erasing The Crossover
One of the biggest questions to come out of The Flash finale is whether Barry's time reset affects other Earths too. If that's the case then everything that happened on Earth-2 in Season 2 of The Flash has now been erased, meaning Zoom's reign of terror is still going strong.
Of course, Barry also visited Kara's Earth (Earth-0? Let's call it Earth-0). So has this crossover episode now been erased, along with the last 14 years of Earth-1's timeline?
The upshot of this (for Supergirl Season 2) is that Kara and the others aren't aware the multiverse exists, and have no memory of Barry visiting them. That would be really annoying, considering the crossover episode was one of the strongest in Supergirl Season 1, but it wouldn't have a huge affect on the show itself.
What it does mean, however, is that Supergirl now has a blank slate as far as Earth-0's introduction to the multiverse is concerned. Discovering the other Earths could be a major part of Season 2, leading up to that giant crossover. But there's another option:
Merging With Earth-1
When Zoom announced his plan to collapse the multiverse, I fully expected Kara's Earth to merge with Barry's, neatly explaining the introduction of Supergirl to the CW's fall roster.
But it's entirely possible that this has happened, and no one realized. Everyone was so busy thinking about Earth-2 that no one really thought of the effects on the other "infinite Earths" in the multiverse. Though that's not really surprising, considering the fact that Barry didn't mention the fact that he'd traveled to a new Earth within a few minutes of The Flash episode "Versus Zoom."
So, here's the theory: Before Barry's time remnant shut down Zoom's doomsday device, what if Kara's Earth did actually merge with Earth-1? That would certainly be an interesting situation for the next season of each shows to explore, as the change wouldn't be apparent at first. We could get lots of hints and Easter Eggs building up to more crossover episodes between the shows — which we've already been promised.
Of course, that might be too complex. It's highly likely though, that Supergirl's full introduction to the CW multiverse will be a major factor in both Season 2 and The Flash Season 3. This could even feed into Legends of Tomorrow, as we still don't know what Earth the Justice Society comes from.
Bear with me, because I'm gonna spin another possibility. If Barry decides — after seeing the changes to his world at the beginning of Season 3 — to undo his decision, this could again have huge repercussions for all the shows. Remember that massive breach Barry created at the end of Season 1? It's possible that in the new new timeline this could have lead to Kara's Earth, meaning that when Barry travels back to the present again, Earth-1 and Earth-0 could have merged.
Or maybe we'll see something totally different. There's a bunch of plot threads from Supergirl Season 1 to contend with too, like the Legion of Super-Heroes and that big cliffhanger about who's in the pod. We could be seeing some big time travel plots in Supergirl Season 2, especially if the showrunners plan to use Superboy to introduce the futuristic Legion. And of course, more time travel could create more alternate timelines.
Anything and everything is possible at this point, but one thing's for certain — the next seasons of all the CW shows are bound to be awesome.