Dementors

A dementor is an utterly foul fictional being, the worst creature J. K. Rowling's Harry Potter book series has to offer (so far), not counting certain humans. They guard the extremely high-security wizard prison of Azkaban.

In appearance, dementors are humanoid figures approximately eight feet in height covered in dark, hooded cloaks which reveal only grey, scabby, decaying hands. They infest the darkest, dankest places and do not breed; instead, they grow like fungi in these habitats ^[1]. Their movie counterparts are considerably shorter, and fly instead of gliding.

The creatures have no eyes. They sense and feed on the positive emotions of human beings, forcing them to relive their worst memories. The very presence of a dementor makes the surrounding atmosphere grow cold and dark, and the effects are cumulative with the amount of dementors present. Those kept in the company of a dementor for too long are often driven insane, which is the main source of Azkaban's well-deserved horrible reputation. Their source of sustenance allows the Ministry of Magic to reluctantly employ them; dementors are at least intelligent enough to be greedy, and to obey as long as doing so provides them with a bigger feast. Dementors are invisible to Muggles and Squibs, but affect them in the same way. The author has herself likened the effect of a dementor to the human ailment known as depression.

The only way to shield oneself from dementors is to use the difficult Patronus Charm to drive them away. The charm summons a patronus, a sort of physical manifestation of good will, which has no despair for dementors to thrive on. Chocolate is an effective first aid to mild cases of contact.

Unfortunately, the feeding is not the worst part. Dementors have an ultimate weapon known as a Dementor's Kiss which quite literally sucks out a person's soul into the mouth of the dementor, a horror to anyone who witnesses it. The victim is left an empty shell, yet not quite dead – just a soulless, gibbering person, incapable of a single thought. The Ministry of Magic seems to occasionally allow this as a punishment.