The Green Slime(1968)
A giant asteroid is heading toward Earth so some astronauts disembark from a nearby space station to blow it up. The mission is successful, and they return to the station unknowingly bringing back a gooey green substance that mutates into one-eyed tentacled monsters that feed off electricity. Soon the station is crawling with them, and people are being zapped left and right!
This is the theatrical trailer for the movie.