The Flash - Season 3 - Eps 17: Duet (II)
Barry and team are surprised when Mon-El and Hank Henshaw arrive on their Earth carrying a comatose Supergirl who was whammied by the Music Meister. Unable to wake her up, they turn to Team Flash to save her. However, the Music Meister surprises The Flash and puts him in a similar coma, one that Team Flash can't cure. Kara and Barry wake up without their powers in an alternate reality where life is like a musical and the only way to escape is by following the script, complete with singing and dancing, to the end. The crossover starts on Supergirl S02E16 Star-Crossed (I).
About The Flash

Title: The Flash
First Air Date: 2014-10-07
Last Air Date: 2023-05-24
Status: Ended
Rating: 7.8/10 (from 11226 votes)
Language: EN
Seasons: 10
Total Episodes: 184
Network: The CW
Genres: Drama, Sci-Fi & Fantasy
Production Companies: Warner Bros. Television, Berlanti Productions, DC Entertainment
Synopsis
After being struck by lightning, CSI investigator Barry Allen awakens from a nine-month coma to discover he has been granted the gift of super speed. Teaming up with S.T.A.R. Labs, Barry takes on the persona of The Flash, the Fastest Man Alive, to protect his city.
Cast

Grant Gustin
Barry Allen / The Flash

Candice Patton
Iris West-Allen

Danielle Panabaker
Khione

Danielle Nicolet
Cecile Horton

Kayla Compton
Allegra Garcia

Brandon McKnight
Chester P. Runk

Jon Cor
Mark Blaine / Chillblaine