Revealing mistake: When the man pushes Leroy's body down the basement stairs, as his body is sliding down, when it's almost to the bottom, you can plainly see Leroy lift his head up as he's sliding, although he's dead.
Continuity mistake: In the very beginning, Fool falls down the basement stairs when the man pulls the lever to make the stairs a ramp. He is wearing a purple and black striped shirt. Later, near the end, Fool goes back into the basement on the same stairs. This time, he is wearing a green shirt. When the man chases him and pulls the lever again, we see the same footage of Fool rolling down the stairs/ramp from earlier (black & purple shirt). When Fool gets back on his feet, his shirt is green again. (01:24:15)
Continuity mistake: When the third Person from Under the Stairs bursts out (from the wall) the Woman is flinching in the corner, pressing up against the wall. As she does she breaks the brown wooden panel in the wall behind her, splitting it in two. In the next shot the wall is back intact. (01:28:45)