The CW has been building up its shared universe of DC Comics-based shows since Barry Allen (Grant Gustin) made his debut on the second season of Arrow before spinning off onto his own series, The Flash. Shortly after the spinoff premiered, the network featured a crossover event between the shows. The following year, The Flash and Arrow combined forces in order to introduce the second spinoff series, Legends of Tomorrow. Now, with Kara Danvers (Melissa Benoist) and Supergirl making the jump from CBS to The CW all four shows are planned to unite for a massive three-hour crossover event.
Additionally, The CW announced plans to feature a two-episode musical crossover with Supergirl and The Flash this fall, which will air after the four-show event. Although Buffy the Vampire Slayer and The Avengers director Joss Whedon is rumored to be involved, nothing official has been announced as of yet. But, Arrow-verse producer Greg Berlanti has offered an update on the musical crossover and teased upcoming announcements.
In an interview with IndieWire, Berlanti was asked about the progress being made on the musical crossover - an idea fans of both Supergirl and The Flash have been anticipating for a while. Berlanti said that the writing team had just finished the big crossover event, but they will be moving on to figuring out the music for The Flash and Supergirl soon. He said:
Next week we’ll have to start talking about clearing music. I have a few ideas for tone and style in my head but we’re just starting to talk about what that can be. I do want to try and get an original piece of music written. As we make a deal on that we’ll probably make some announcements on the original songs.
Although Berlanti didn't mention any names of songwriters who could potentially be tapped for the project, he was asked if Hamilton's Lin-Manuel Miranda could be involved. The producer laughed and said they were "pretty close" to making an announcement about the original music for The Flash and Supergirl crossover. However, he did offer a tease as to the identity of the songwriter:
I can’t say yet because we don’t have a deal yet, but I did speak to someone we’re really excited about. There are some writers I’m incredibly excited to work with.
Along with the report that Whedon would be directing the two-episode musical crossover, it was rumored that Supergirl and The Flash were planning to include the DC Comics villain Music Meister, an antagonist from Batman: The Brave and the Bold who can manipulate his victims into singing and dancing. Additionally, it has been speculated that The CW would approach Neil Patrick Harris - who voiced the character on the animated series - for the role. However, fans have suggested Miranda himself as a potential actor suited to the villainous role.
That said, as Berlanti indicated, it's still early on in the production process for the musical crossover episodes, so it remains to be seen which villain will be included, who will play the part, and who will be tapped to work behind the scenes on the music. But, the previous crossover between The Flash and Supergirl was met by a largely positive response and the musical episodes may be as well received - especially if they include quality original songs.
The Flash season 3 will premiere Tuesday October 4th at 8pm on The CW, Arrow season 5 will premiere in the same timeslot on Wednesday October 5th, Supergirl season 2 on Monday October 10th, and Legends of Tomorrow season 2 on Thursday October 13th.