Understandably, creating a movie poster isn't easy. There have been plenty of bad films that have received jaw-dropping one-sheets everyone wanted in their room and plenty of terrible posters you wouldn't touch with a ten-foot barge pole that were made for incredible movies.
It's a tough balancing act: artists need to sell an audience on what they're about to see, convey the tone, highlight the characters and actors and generally give off some kind of appealing vibe to get backsides in seats. When it goes wrong, we get abysmal posters like the ones for X-Men: First Class, but when it goes right we get an Empire Strikes Back or The Thing.
The art of the film poster stems beyond pure surface level appeal though, and over the years marketing departments have - accidentally or otherwise - included some pretty major spoilers for the movie they want everyone to see.
Sometimes this is subtle and something that'll make you go 'aha!' afterwards, but sometimes it's a blatant bad move on the studio who, for whatever reason, decided to give away too much.
9. The Prometheus Has... Crashed? - Prometheus
A lot of sci-fi movies - especially in a post-Cloverfield world - are built around marketing campaigns that are shrouded in mystery. That went double for Prometheus, Ridley Scott's decades-in-the-making return to the Alien franchise.
The trailers only gave us vague hints at the story: What was the goal of the Prometheus ship and its crew? How was this story connected to the events on the Nostromo? Who were the Engineers? Very little was explicitly revealed about flick's big set-pieces too, apart from one poster which showed the Prometheus itself exploding into the side of the Engineer's spaceship.
Now if you remember the movie, this moment is a pretty monumental third-act set-price that leaves a couple characters dead and our heroes more isolated than ever. If you saw this poster though you'd spend much of the film waiting for it to happen, waiting for the Engineer ship to reactivate and for the tension to be sucked out when Scott teases that it might make it off the planet.
The artists clearly tried to avoid making it too spoilerific - including characters underneath who aren't actually present in that scene - but while the specifics may be off, a version of the scene does still takes place.