Boogeyman (Don't Look Under The Bed)

When a child stops believing in an imaginary friend too soon, the friend is unable to move on, and will often transform into an evil boogeyman. In most cases, a boogeyman will age and fade away after a child grows up sufficiently, but this is not always the case. A boogeyman can be returned to their original, friendly form if their former friend believes in and accepts them once more.