Ok, ok, ok, why does Superman have a mustache? Basically, he’s shooting both Justice League and Mission Impossible 6 at the same time.
This wasn’t the original plan. Cavill was supposed to be finished with shooting MI6 before the Justice League reshoots began. However, it didn’t quite work out that way, which is why Warner Brothers is now having to digitally remove Cavill’s MI6 stache from the Justice League.
Supposedly, Paramount will not allow Cavill to shave his face while filming MI6. However, neither of the studios have commented in the issue.
Maybe they should just leave it in. It would certainly help with that whole Clark Kent cover.