CW's The Flash and Supergirl - Musical Crossover

The Flash and Supergirl already planned a crossover and now we know it's going to be a musical crossover. Executive producer Greg Berlanti confirmed a "musical pair of episodes in the back half of the year". They plan to be careful about how the characters sing and it could take place in their minds, at times. They are still planning another crossover between The Flash, Supergirl, Arrow, and Legends of Tomorrow for December 2016.