A Sincere Warning About the Entity in Your Home

This short horror story takes the form of a warning letter, supposedly sent to your own address by the previous resident of the house you've just moved into. Over several pages, he lays out exactly what he went through with an entity that preyed on him in that house, an ordeal that nearly consumed him before he found a way out. He's sorry to be leaving the problem for you, but he's found his loophole, and it's your turn now. The epistolary format is the hook: it presents itself as a real document meant for the reader specifically, which is part of why it has such a strong reputation as an effective piece of short horror fiction.