Sony's hit Venom movie very nearly had a totally different opening sequence and origin for the alien symbiote. The film opened with a space shuttle for the Life Foundation crash-landing to Earth after a mission in space, carrying one of the alien symbiotes in a canister. When a cleanup crew comes to claim the canister, they find that one of the astronauts is already infected by a symbiote, which then leaps from him to another host before escaping.
In an interview with CinemaBlend, director Ruben Fleischer reveals the alternate opening that would have taken us all the way to a distant symbiote planet, and would have gone into greater detail about what they are...
To be honest, I missed the opening few minutes at our screening and had to catch up with it later. When I did it didn't seem like I had missed all that much. The introductory sequence worked at keeping the symbiote mysterious, but it didn't really stand out as crucial to the story. I think it was probably the best way to go for long-term story planning (and for keeping the budget down) and going to an actual symbiote world would have cut off a potentially cool future storyline.