I didn't know who
Mr. Mxyzptlk: is. I stumbled on the name and so I looked him up. Here's what I found:
He's a magical imp jester from the fifth dimension.
He appeared at first as a small bald man in a purple suit, green bow tie, and purple derby hat. But later he grew some hair and changed his color to orange.
By mistake, his name also got changed to Mr. Mxyxptlk.
Some clever blokes decided to explain the mistake by saying the two were actually different, and that one was an "Earth-1" version and the other was "Earth-2". Please.
Lex Luthor eventually taught him how to lie.
Mr. Mxyzptlk became an instrument for post-modern self-deprecating, self-referential humor, breaking the fourth wall and commenting wryly on editorial decisions and genre cliches.
Earth-1 version has a girlfriend named Ms. Gsptlsnz.
In the live-action TV show "Superboy", he is said to be a leprechaun.
This is how Superman sent him back to the fifth dimension (Click to enlarge):
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