Superman, Mxyzptlk and... Watchmen (sort of)

Above page 11 and 12 from Adventures of Superman n. 496  - published in 1992 by DC Comics - where Mxyzptlk shook Superman's reality adding a bit of... Watchmen too! 

Story by Jerry Ordway and Dennis Janke. Art by Dennis Janke.

More info here, too.