There are only so many horror tropes to draw on: Killer aboard spaceship knocking people off; killer robot aboard spaceship knocking people off; killer robot mutant aboard spaceship knocking people off; alien aboard spaceship knocking people off; vengeful host of alien, which lives on in a now killer robot, knocking people off.
Replace ‘spaceship’ with a house, or an American Indian burial ground, or wherever, twist the other elements about, and you have pretty much every horror movie ever made.
Which is why how you approach the subject matter is just as important as the subject matter itself.
“The Babadook” appears to take a well-worn idea: a child fears things that go bump in the night, and extrapolates it into the mental disintegration of not only the child, but the parent.
There’s even logic to the title, which doesn’t stop it from being not terribly good anyway.