Mr. & Mrs. Mxyzptlk

"Mr. & Mrs. Mxyzptlk" is the thirteenth episode of the second season of Supergirl, and the thirty-third episode overall. It aired on February 20, 2017.

Synopsis
When Mr. Mxyzptlk, a magical imp, shows up on Earth and declares his love for Kara, 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 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 and Maggie celebrate their first Valentine’s Day together.

Trivia

 * Mr. Mxyzptlk tries to serenade Kara by briefly singing "A Whole New World" from Aladdin.