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The Symbolic Hybrid variation
These are always interesting. Even when they're not that great, they're certainly more appealing than the Floating Heads.
By creating a hybrid of two objects, whether they're people mixed with things, things mixed with things, or things that pile up to make another thing, the merging of the two forces you to evaluate what each thing is separately, and then what they mean together. That meaning speaks to some core element of the film.
Depending on the movie, they can't be too oblique. If there's one thing marketing departments try to shy away from, it's making the viewer feel stupid. But art house films can be a bit more obscure.
Take that AntiChrist poster, for instance. Everything about it is disturbing. It's an incredibly strong image. But what does it mean? Well, since I haven't seen it, I can speculate only with what I've read about it. I know, for one, that there is a pretty brutal scene involving scissors. Hence, the scissors and the blood. That stream of blood is also very strategically placed. I know that it is about a couple (Willem Defoe, Charlotte Gainsbourg) and that it gets pretty erotic at certain points. I also know that it messes with your head. It's a horrific and surreal experience. All of that is hinted at with this one bizarre image. So, though it is referencing a plot element that those who haven't seen the film won't catch, it is a very successful representation of the content.
The same goes for the rest of these examples. They are all capable of not only representing content, but also the attitude or tone of the films.