The fifth-dimensional being Mxyzptlk returns with an offer to let Kara change her past and make things right with Lena. But the alternate histories could make the world as she knows it even worse.

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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).