Melissa Benoist stars as Kara, and is joined by principal cast members Chyler Leigh, Katie McGrath, Jesse Rath, Nicole Maines, Azie Tesfai and David Harewood.
The episode sees Kara travelling back to various points in time with Mxyzptlk's help to find a way to repair her relationship with Lena Luthor.
Several former series regulars make guest appearances, including Chris Wood, Jeremy Jordan, Sam Witwer and Odette Annable.
Nia Nal saves them from a Hope-Bot and brings them to Alex, J'onn, Winn Schott, Mon-El and Kelly Olsen.
[1] The episode, which is the series' 100th, was directed by Jesse Warn, and written by Derek Simon & Nicki Holcomb from a story by showrunners Robert Rovner & Jessica Queller.
[1] Jeremy Jordan, who portrays Winn Schott, described the episode as "a love letter to our fans for always supporting us [...] We get to revisit some of these great moments we've had over the course of the series and make some fun new memories.
"[6] Main cast members Melissa Benoist, Chyler Leigh, Katie McGrath, Jesse Rath, Nicole Maines, Azie Tesfai and David Harewood appear as Kara Danvers / Supergirl,[2] Alex Danvers,[7] Lena Luthor,[2] Brainiac 5,[6] Nia Nal / Dreamer, Kelly Olsen, and J'onn J'onzz / Martian Manhunter respectively.
[8] Former regulars Chris Wood, Jeremy Jordan, Sam Witwer and Odette Annable guest star as Mon-El, Winn Schott, Ben Lockwood / Agent Liberty and Samantha Arias / Reign respectively.
[10] The showrunners wanted former regulars Mehcad Brooks and Calista Flockhart to guest star as James Olsen and Cat Grant respectively, but the actors could not appear due to scheduling conflicts; Brooks instead appears as his character via archive footage, and Flockhart through a photograph, with Rovner explaining, "even without them being available, we wanted to make sure that they were a part of the episode".