During the weekend, it was confirmed by Greg Berlanti during the recent TCA (Television Critics Association) event that the upcoming Supergirl / The Flash musical crossover will be featuring the Music Meister. The character first debuted in Batman: The Brave and the Bold voiced by Neil Patrick Harris. Currently it is not confirmed that he will be reprising the role in the CW verse however, according to Berlanti he stats that the team is “… certainly huge fans of him and as the casting process proceeds we’ll see what happens.”
Andrew Kreisberg also had some statements about the upcoming crossover as well.
“Hearing Melissa [Benoist] and Grant [Gustin] sing. … I hear Melissa sing all the time, so for you guys to hear that finally will be so great. As much as we hope these shows speak to people, whether socially or Alex’s storyline and what it means to people, at the end of the day we’re trying to entertain people. … To be able to do a musical episode is so exciting to us. If anything, it’s what I would always love about what Joss Whedon would do [on Buffy] with “Hush” or “The Body.” He’d have these very special episodes, but they were intrinsic to the ongoing storytelling that was going on.”
Source: IGN
