Superman #50 DC ⋅ 1990

Clark Kent proposes to Lois Lane, she accepts

Marvel/DC crossover: Mr. Mxyzptlk reveals himself to also be Marvel’s Impossible Man and claims he needs to visit his ‘four friends’

Quote 'Oops, sometimes it's just IMPOSSIBLE to remember what I look like from world to world’

In this issue, he confronts a group of heroes dressed in blue using dialogue from the Impossible Man's first appearance (Fantastic Four #11 - 1963)

I'm not a professional grader.

Reference is from key collector. key collector is in USD$