10. Suicide Squad
You need only compare the rapturous response to Suicide Squad's trailers to how coldly the final film was received to appreciate how drastically David Ayer's ensemble comic book flick was tinkered with during post-production.
The initial marketing push implied Suicide Squad to be a gritty men-on-a-mission movie, boasting a level of edgy attitude that seemed to suit the characters - contrasted from the inappropriately downbeat tone of Zack Snyder's Man of Steel and Batman v Superman. The first trailer also played-up the presence of Jared Leto's insidiously playful Joker.
After the vitriolic response to Batman v Superman, however, Warner Bros. decided to change the tone of the movie's marketing, even while they were still unsure of quite what tone they wanted the movie itself to have.
Consequently, later trailers implied a lighter affair more in the vein of Guardians of the Galaxy, with an emphasis on witty one-liners and liberal use of pop music.
At this time, the studio was still wrestling with Ayer over the tone of the blockbuster, resulting in a baffling six (!) different cuts being assembled, in the hope of finding a compromise between Ayer's hard-edged version and the studio's panic-stricken desire for something frothier.
The final cut of Suicide Squad ultimately wasn't reflected by any of the film's trailers, however - it was a tonal car crash which attempted to combine the battling creative philosophies into a whole that patently didn't fit together.
Moreover, for fear over the backlash against Leto's performance, The Joker ended up being relegated to an extended cameo, with most of his trailer scenes being cut entirely.
The memorable glimpse of a wounded Joker pulling a grenade pin with his mouth, for instance, was part of a lengthy encounter with the titular team that ended up on the cutting room floor.
Elsewhere, countless sequences were removed from the theatrical cut, including scenes exploring Rick Flag (Joel Kinnaman) and Dr. Moone's (Cara Delevingne) relationship.
Though many fans were hopeful that Suicide Squad would serve as an apology for the disaster that was Batman v Superman, it reminded fans just how effortlessly a well-cut set of trailers could disguise massive production problems.