Goofs

The exterior and layout of the mansion changes from the first time the group of youngsters come upon it and then later when they are trapped inside. It is clearly two very different buildings.

When the decapitated head of Abigail is on the floor and screaming, you can see the floorboard moving up and down, clearly showing that they are in fact not wooden floorboards at all.

When the two last survivors are sitting on the floor after defeating the girl, a shadow of a wire can be seen behind the survivor on the left.