Warning: spoilers ahead for Episode 11 of The Flash Season 3.
The CW's DC universe has already featured some epic superhero team-ups in the 2016-2017 TV season. The massive "Heroes v. Aliens" event brought protagonists from four shows together for the first time, and the upcoming musical extravaganza between The Flash and Supergirl has been getting buzz for months. In the latest episode of The Flash, however, viewers got a crossover that nobody could have seen coming. As Cisco was traveling between Earths in a battle with Gypsy, their brawl popped out into Earth-38 in a place that Supergirl fans recognized immediately: CatCo. Take a look!
The Flash called upon Cisco to use his powers as Vibe to battle the Earth-19 collector known as Gypsy, who made her way to Earth-1 to retrieve H.R. for breaking the Earth-19 law forbidding travel between universes. The penalty for breaking that particular law is death, so Team Flash rallied to save their pal, resulting in Cisco offering to battle Gypsy in a trial by combat for H.R.'s life. The two vibers began a duel that sent them tumbling between dimensions, which took them briefly to Earth-38, where they scared the bejesus out the office staff.
The major characters of Supergirl were nowhere to be seen, so we can guess that they were occupied with superhero shenanigans of their own. The office currently belongs to James Olsen (after the departure of Calista Flockhart's Cat Grant), but he was probably too busy working as Guardian to keep up with his CatCo paperwork. Hopefully Kara gave him a rundown of the good guys she she met on her trip to Earth-1, because James might need to find a way to calm down a very panicky CatCo underling.
Cisco and Gypsy popped out into other worlds as well. In addition to Earth-38, they fell into Earth-2 and a place that looked suspiciously like Mustafar. We didn't get any crossovers to Arrow or Legends of Tomorrow, but the Supergirl glimpse was pretty great. Supergirl is the one show in The CW's DC universe that actually exists on another Earth, so crossovers with Kara and Co. generally don't happen, but Cisco's Vibe powers made the crossover logistically possible, thus our peek of CatCo in this week's episode of The Flash.
The next Flash/Supergirl crossover that we know about will be the musical two-parter, which begins on Supergirl on Monday, March 20 and concludes on The Flash on Tuesday, March 21. We'll have to wait and see if we get any more quickie crossovers beforehand. Barry has plenty on his plate as he tries to figure out how to train Wally to become fast enough to save Iris. Still, anything is possible on The Flash.