Supergirl may want to closely examine any flowers she receives on Valentine's Day when the classic DC Comics antagonist Mr. Mxyzptlk pays her a visit in "Mr. & Mrs. Mxyzptlk."

RELATED: "Supergirl" Casts Peter Gadiot as Mr. Mxyzptlk

As we learn in the description for the Feb. 20 episode of "Supergirl," while Mon-El (Chris Wood) and Kara (Melissa Benoist) disagree on the best way to handle the magical imp, Alex (Chyler Leigh) and Maggie (Floriana Lima) reach a pivotal moment in their relationship: their first Valentine's Day as a couple.

DC COMICS’ MR. MXYZPTLK HITS NATIONAL CITY – When Mr. Mxyzptlk (guest star Peter Gadiot), a magical imp, shows up on Earth and declares his love for Kara (Melissa Benoist), she tries to let him down easy, thinking him harmless. However, he decides it’s a challenge and starts to wreak havoc on National City. Mon-El (Chris Wood) has seen beings like Mr. Mxyzptlk on Daxam and knows how dangerous they can be. He and Kara argue over how to get rid of Mr. Mxyzptlk, further straining their relationship. Meanwhile, Alex (Chyler Leigh) and Maggie (Floriana Lima) celebrate their first Valentine’s Day together. Stefan Pleszczynski directed the episode written by Jessica Queller & Sterling Gates.

Introduced by writer Jerry Siegel and artist Ira Yarborough in 1944’s "Superman" #30, Mister Mxyzptlk is a mischievous imp from the fifth dimension who delights in tormenting the Man of Steel. More fun-loving prankster than straightforward villain, Mxyzptlk’s fifth-dimensional technology appears as magic to three-dimensional beings; the limits of his powers are vast and unknown. Famously, he can only be stopped and returned to his home dimension by tricking him into saying his name backward (“Kltpzyxm”).

Airing Mondays at 8 p.m. ET/PT on The CW, "Supergirl" stars Melissa Benoist, Mehcad Brooks, Chyler Leigh, Jeremy Jordan, David Harewood and Chris Wood.