On February 23, and 'Supergirl' completed 100 episodes since its start in 2015. Ahead of the episode, The CW released a preview of Episode 13: 'It's a Super Life', which sees the return of Mxyzptlk (played by Thomas Lennon), who offers Kara/Supergirl (Melissa Benoist) a chance to find out what it would have been like had she told her secret to Lena Luthor (Katie McGrath) instead of Lex Luthor (Jon Cryer).

The Kara-Lena relationship has been one of the highlights of Season 5 and was followed by Arrowverse's epic crossover, 'Crisis on Infinite Earths'. Lena discovering that Kara was Supergirl ended the duo's friendship and with Earth-Prime being the result of the multiverse-shattering battle, she decides to work with Lex in the new reality that was formed.

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100 episodes later and we love this show more and more every day ✨ How excited are you to see the 100th episode of @supergirlcw tonight? ⁠ ⁠ ⁠ ⁠ ⁠ ⁠ ⁠ ⁠ ⁠ ⁠ ⁠ ⁠ ⁠ ⁠ #MelissaBenoist #AzieTesfai #JesseRath #DavidHarewood #ChylerLeigh #AndreaBrooks #LenaLuthor #Supergirl #CrisisOnInfiniteEarths #COIE #Arrowverse #TheFlash #Arrow #cwsupergirl #NicoleMaines #Dreamer #supergirl #cw #cwsupergirl #karadanvers #karazorel #kara #alexdanvers #monel #karamel #chriswood #girlofsteel #melwood #KatieMcGrath #Supercorp

A post shared by TV Guide (@tvguide) on Feb 23, 2020 at 7:40am PST

The official synopsis reads: THOMAS LENNON (`RENO 911`) GUEST STARS IN SUPERGIRL'S 100TH EPISODE - Mxyzptlk (guest star Thomas Lennon) returns with a proposition for Kara (Melissa Benoist) - what if she could go back in time and tell Lena (Katie McGrath) her secret before Lex did, would things turn out different? Looking back over key moments throughout the series, Kara must decide if she wants to change history to become friends with Lena again. Familiar faces return in this special episode. Jesse Warn directed the episode with story by Robert Rovner & Jessica Queller and teleplay by Derek Simon & Nicki Holcomb (#513).