Aliens, from Alien
Aliens might just be the weirdest characters in the history of film. They start as fleshy-crab like creatures that attach to a victims face releasing a fetus into the digestive system of a still living human. After several hours of feeding off the nutrients inside the hosts body, it bursts though the chest cavity and matures into adulthood quickly. The great Swiss surrealist H.R. Giger designed the now legendary look which has been often imitated in and out of the movie world but, never to such a terrifying effect.