What really scared me was an episode of Space 1999 called DRAGONS DOMAIN. A tentacled monster with a glowing eye that howled or screams would grab with its tentacles, shove you underneath and you would come back a smoking husk of a body. It could materialize inside your ship and phasers did not work on it. I am now an adult, I bought the episode and it still creeps me out
Oh, I remember that one! Absolutely terrified me and I think I might have just stopped watching the show, as I don't remember any other episodes. I think what really got to me was the guy's wife screaming when his burnt, smoldering body was returned to the ship.