One of the more peculiar stories to rise up during Joss Whedon's Justice League was the story that Henry Cavill's mustache, facial hair he had grown for his character in Mission: Impossible - Fallout, would have to be digitally removed since Paramount wouldn't allow him to shave it. It was merely an interesting, eyebrow-raising story at the time, just another quirky story from the set of a troubled movie. Little did we know that mustache would come to be one of the most talked about aspects of Justice League.
Despite criticism of Zack Snyder as a storyteller, most people can agree that he's one of the best directors in the game when it comes to visuals. So, while some people figured they may not like the overall aesthetic or story with Justice League, the idea of the movie's VFX being poorly executed was never really on anyone's radar. Fans have lodged numerous complaints with the lighting, colors, as other stylistic decisions of Batman v Superman, Man of Steel, Watchmen, 300, and most other Snyder movies, but the complaints are almost exclusively with the artistic design, not the actual execution.
So, obviously, it was a bit of a shock when Justice League arrived in theaters, leading with a very poorly rendered shot of Henry Cavill's CGI mouth. The problem would extend to Steppenwolf's CGI, bad reshoot green screen, CGI corn, bad cape effects, video-gamey Apokaliptian terraforming, and more. For a franchise whose one saving grace has been that most people could agree that "well, at least it looks good," the poor effects were just another element of the Frankenstein project of Justice League. With a number of low-quality shots of Superman's awkward looking mouth circulating on social media since release, some people wondered if maybe the effects would look better on the official release. Now that Justice League is out for digital home release, that's clearly not the case. After other good-looking films in the franchise, how did this happen?
A Rushed Schedule Ruined Justice League's CGI
The most obvious explanation for the poor VFX is Justice League's rushed schedule. Before he was fired, Zack Snyder had achieved picture lock on his cut of the film and was already working on finalizing some VFX shots, but his version of the movie was mostly scrapped for footage reshot by Joss Whedon as late as August 2017, just 3 months prior to the movie's release. This means 2 things. First of all, VFX teams that had to wait for final footage before completing their effects had little time to polish and finalize their work, making most of the VFX shots simply a "best effort" endeavor with the VFX artists doing the best they could do, simply lacking the time needed to provide the same quality they have in the past.
The second impact of the protracted reshoot schedule is that the movie's digital intermediary, or color grading/color correction process was not completed until late in the game. Typically DI is completed after picture lock is achieved, before the VFX are completed or added, with the VFX artists simply matching their work to the colors and shading of the final footage. Because of the reshoots, Justice League's color grading was just being completed in mid-October, only a few weeks before the movie hit theaters. This means that most of the VFX shots would have been completed prior to DI, which can result in rough edges being exposed by changes to light, shadows, and color. It's possible some VFX work, including mustache removal, looked absolutely fine when the VFX teams handed them off, but when some scenes were significantly brightened (some were changed from nighttime to daytime) or had saturation boosted, the work that originally looked fine could have no longer blended well, resulting in visuals that stand out in clear uncanny valley territory unnecessarily.
Warner Bros. Apathy Meant Low Standards
One of the more disappointing reports to come out after Justice League's release was that Warner Bros. expected the film to see a poor reception and didn't want to take measures, such as pushing back the release date, to improve the final product. This means the standard had long since lapsed from "quality movie" to "good enough."
Without Zack Snyder at the helm, the movie was instead guided by producer's and a director whose objective was simply to get the movie out the door, meaning the desire time and effort needed to maximize the quality of each VFX shot was completely gone. This is especially visible in some of Superman's CGI cape shots where the cape flapping in a light breeze is more reminiscent of a plastic bag than any type of draping fabric. One or two moments of low quality like this can be expected in most movies, but when a VFX heavy project has its schedule shorted, has color grading completed after VFX is already added, and has a low standard of quality from executives, it's going to make for one ugly movie.