There are specific reasons why alternate versions of Arrowverse characters haven't been featured in Supergirl

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Shows like The Flash and Arrow have included alternate versions of different heroes, like the Earth-2 version of Deadshot showing up on Arrow. While speaking to IGN, Supergirl producer Andrew Kreisberg was asked if viewers might ever see Earth-1 versions of the Supergirl characters pop up on Flash and Arrow, or different versions of the Arrow, Flash or Legends of Tomorrow pop up on Supergirl.Kreisberg explained that the show's producers decided not to mess with alternate realities on Supergirl for fear of muddling the narrative and not having a good enough story reason."The problem with that is it feels to us like if we do that once, we're going to open the floodgates of insanity," Kreisberg. "It's like Supergirl's over here, and it's its own show. Technically speaking, it's just another Earth, the same way Earth-2 is or Earth-3 or Earth-19. So technically speaking, there should be an Alex Danvers on Earth-1, or Earth Prime. But if we start doing that, I just feel like… Not that all hell hasn't broken loose already, but unless we had a really good story for it..."Kreisberg believes you can easily turn these alternate worlds and heroes into an overused and boring gimmick."The more you start to do that stuff, the more it can very easily become annoying or like, “'Here we go again,'” Kreisberg said. "Even on Supergirl itself, like Chyler [Leigh] got the opportunity to play a White Martian [impersonating Alex]. Already built into our show, there's already characters playing different versions of themselves. It could very easily spiral out of control."While alternate versions of familiar characters doesn't seem to be in the cards, Supergirl is still set to team up with her fellow Arrowverse heroes. Read up on how CW's next big DC crossover will feature all four shows

Alex Gilyadov is a freelance writer for IGN. You can follow him on Twitter.