Supergirl S02E13, A magical imp called Mr. Mxyzptlk arrives on Earth and wreaks havoc on National City when Kara doesn’t reciprocate his feelings.

In Supergirl S03E06: Midvale, Back to Midvale High School, Alex & Kara have a mutual friend, she is murdered by her teacher, after effort on killing them failed, the teacher was arrested. But they also found out that someone who is drug dealer in accusing for killing their’s friend.