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I saw a movie or TV show when I was a little child in the 80s. It had a low budget, 70s look. I can remember only two scenes from it.
In the first, there is a guy with a cow boy hat and a gun, Magnum like; I think he was inside the typical American dinner restaurant. He shoots an alien. The alien wears a tunic and some sort of metallic triangular helmet pointing downwards. When he is shot, his body seems to disappear, and his tunic and helmet fall to the ground.
The other scene is about a vessel, like a caravel, sailing through the desert, not water, with some people on it. Maybe, the guy travelling on it is the same one who shot the alien.