The "Justice League" reshoots, which wanted to accommodate with the success of "Wonder Woman" among other things, cost the WB upwards of $25M, with Joss Whedon, who took over Zack Snyder's leave of absence, overseeing it all. Those reshoots dragged on for roughly two months. It wasn't just reshooting scenes that plagued the film, it was also the fact that Henry Cavill's was a major issue for the filmmakers. “Justice League” was expected to finish shooting before the sixth “Mission: Impossible” film, starring Cavill, was tobegin production. Sadly, this being DC and production issues always seeming to be a problem, the new scenes that were being shot required Cavill to jump back and forth between films. Having to sport a mustache he grew for his character in the “Mission: Impossible” sequel, Paramount, which was in charge of MI:6, would not allow Cavill to shave his 'stache in order to shoot his scenes as Superman for "Justice League." The WB, with not many options to show for, figured the only option they had was to just digitally remove the facial hair in post-production.
The very idea of them digitally removing Henry Cavill's mouth brow was a running joke for many fans and, surprise surpise, a major qualm for the many more that saw "Justice League." If you look closely you can definitely see the CGI erasement, of course, one can just let go and, you know, watch the film instead of focusing on Cavill's upper lip, but it turned out to be quite the distraction for many.
Over on Reddit, the VFX artist in charge of Cavill's mustache said the WB offered Paramount the option to digitally create a CGI mustache for the Mission: Impossible film, in return for Cavill to shave the damn thing. It was obviuously a pain and very complex process to digitally remove the mustache, but Paramount didn't budge, they said Cavill keeps the lip rug:
“A mix – to some people it’s a cool little project to get stuck in to and another problem to solve, which is what a lot of VFX is about. Challenging. To me, as a fan, I was annoyed haha Paramount should’ve shaved him and stuck a fake one on for MI6. Ridiculously petty of them. We did tests on already shot footage of Superman to add a beard as well to show the MI6 team at Paramount it was loads easier, and Warner Bros offered to pay for all the beard adding shots in MI6. They said no.”
How important could the dirty Sanchez Cavill was sporting be for the plot of "Mission: Impossible 6"? We won't really know until the film is released next summer, but suffice to say it was important enough that the WB had to go through a digital removal of it and be the butt of jokes of many film fans.
The results are, quite frankly, frightening
