Before Grant Gustin became the scarlet speedster, he played Sebastian Smythe, a villain of sorts and member of the a cappella group the Warblers vying for the affection of Blaine (Criss). Before Melissa Benoist became the woman of steel, she played Marley Rose. Her duet performance of “Holding Out for a Hero” while wearing a superhero outfit even predicted her upcoming casting in the Arrow-verse:
Gustin spoke about possibly bringing Criss into the Flash fold during a 2015 interview with Entertainment Tonight, saying, “I’m like, ‘Dude, we gotta get you on this thing.’ I don’t know in what capacity, but he’s got to.” Now it’s official.
According to TVLine, Criss, Gustin, and Benoist will all sing in the episode, along with Carlos Valdes (Cisco), Jesse L. Martin (Joe), Victor Garber (Dr. Stein), John Barrowman (Malcolm Merlyn), and Jeremy Jordan (Winn), most of who have Broadway experience. The crossover will begin towards the end of Supergirl on Monday, March 20th, but most of the musical action with be saved for the “Duet” episode of The Flash on Tuesday, March 21st. Dermott Downs will direct, and the producers of both shows have said the episodes will come at a “pivotal” moment for each.
Music Meister was voiced by Neil Patrick Harris on the animated series Batman: The Brave and the Bold, where he used his ability to control minds through music to cause mayhem. Executive producer Andrew Kreisberg said of Criss’ casting:
With our Flash and our Supergirl being Glee alums, how could we not have them go up against another Glee favorite like Darren Criss? We have been blown away by his talent over the years and we can’t wait to see what he brings to the Music Meister.