The DC multiverse is many things — complex, filled with infinite possibilities, and convenient if the DC higher-ups want to reboot the whole continuity (again). For the #Arrowverse, the multiverse has yet to be ultilized to its full potential, but the current crossover arc is a good start.
Invasion! kicked off in the last episode of #TheFlash, and we all reveled in nerdy delight as Barry assembled his team of Super Friends — and his first stop was Earth-38, to bring Supergirl into the fray.
If nothing else, The Flash episode "Invasion!" proved that Supergirl plays very well with others, and we're hoping for plenty more crossovers in the future (especially with the #LegendsOfTomorrow).
According to exec Andrew Kreisberg, we've only scratched the surface of the multiverse's potential. And somewhere out there, on Earth-something-or-other, there's another version of Kara Zor-El — one that fans are eager to meet. When asked if we could ever see Power Girl in Supergirl, this was Kreisberg's response:
"We hadn’t discussed it formally, but I think that certainly after these three episodes, there’s literally no limit to the things that we could do. There’s still an endless treasure trove of DC Comics characters, and stories, and titles that we haven’t even come close to touching yet. We’re certainly not wanting for ideas for the future. We know that they’re out there for us."
Power Girl is a very interesting character. She's the Earth-2 version of Supergirl, older and technically a refugee from a destroyed Earth. Her origins are very complicated, and have been retconned multiple times, so suffice it to say that she's Kara's older (bustier) doppelgänger, a bit more worldly-wise and prepared to do what's necessary to save the day — even if that means compromising the morals of her younger self.
Naturally, this would be an interesting element to introduce to Supergirl, and thanks to the multiverse it's totally possible — especially if The CW are thinking of adapting Crisis on Infinite Earths.
Super-Fam & Other Heroes
But Power Girl isn't the only character in the Super family, and we can take Kreisberg's statement to mean that literally anyone and anything from DC Comics is open to appear in the Arrowverse. So here are some more heroes and villains we may see soon in Supergirl...
The Legion Of Super-Heroes
The futuristic team of heroes has already been hinted at in Supergirl Season 1.
The Legion ring in the Fortress of Solitude implied that when Superman was Superboy, he worked with these heroes from the 23rd century, as he did in the pre-Crisis comics. The Legion are a really interesting team, and it would be nice for Supergirl to meet other heroes from her universe too. And speaking of young Kal-El...
With Cadmus playing a major role in Season 2, it's entirely possible that we'll see Superboy soon.
In the post-Crisis comics — and the Young Justice TV show — Superboy was retconned to be a clone created by Cadmus for typically villainous purposes. This would be cool to see, but because we've already got the Cadmus-created Cyborg Superman, it seems unlikely that we'll see the clone Kon-El. However, Cadmus do still have some of Kara's blood, so they could always clone her, which would be an interesting twist on the Power Girl story.
This one's a little off-the-wall, but who doesn't want to see Melissa Benoist's Supergirl team up with DC's version of the Punisher?
Lobo was introduced in the 1980s, and the grizzled biker vigilante hero soon chimed with fans of grittier antiheroes. So far, Supergirl has mostly dealt with strictly hero or villain types, and no-one really blurs the lines between the two. After Kara's dynamic with Heatwave, it would be awesome to see her team up with a similarly morally grey character on her Earth.
With Maggie Sawyer joining the gang in Season 2, we're holding out hope that her comic-book fiance might appear sometime.
Batwoman is a fascinating character, dealing with the very real demons and monsters of DC's mythology. She's dark and brutal, sometimes short sighted in her crime fighting, but also passionate and dedicated to protecting the downtrodden. She would act as the perfect foil to the optimistic and ever-idealistic Supergirl — and it would be great to see Maggie quietly freak out as her ex-girlfriend and current girlfriend finally meet.
Hey, if Batman exists somewhere in this universe, maybe his cousin does too.
Krypto the Super Dog
You didn't think we could get through the list without mentioning Krypto, did you?
This one seems super unlikely, but Krypto is a beloved (if outdated) DC character who even got his own cartoon. Here's hoping he'll at least make a cameo in Supergirl someday.
And the rest...
Then of course there's the oft-referenced bigger DC heroes — Green Lantern, Batman, and many others — whom fans would love to see. As Kreisberg says, there's always the possibility that these Justice Leagers will show up someday, but the licensing of these characters is tricky, so maybe don't hold your breath.
Who would you like to see appear in 'Supergirl'?