4) Supergirl
Supergirl and The Flash are perhaps the most well-matched superheroes in the Arrowverse, as proven by the “Worlds Finest” episode of Supergirl’s first season in which Barry arrived on Kara’s Earth. The two of them are both largely optimistic superheroes and Melissa Benoist and Grant Gustin have terrific chemistry together.
Now that Supergirl is moving to The CW, we’ll hopefully see a lot more of these characters teaming up. Whether a Flashpoint-type reboot realigns Supergirl and The Flash into one universe or they open more multiversal breaches, it just has to happen.
The first order of business should be to have Kara crossover onto The Flash to repay the favour. We think she would slot in to the STAR Labs team like a house on fire. And if she brought The Martian Manhunter with her – so we could have two founding members of the Justice League on screen together – that would make it all the more exciting for fans.