Demons (or Inferi) are magical beings that are motivated by evil who seek to kill innocents and the forces of good. Almost all demons are immortal, though some require additional powers or rituals to sustain their immortality.
Most demons seem to keep the appearance of an ordinary human, either by nature or with magical help. It is also common for a demon to possess a primordial form rather than a physical form that requires forcefully taking control of the body of a living person to manifest on Earth.
The death of a demon is generally referred to as "vanquishing the demon." Some demons require a specific spell, sometimes needing to be blessed by the Power of Three. While most vanquishes are usually instantaneous, there are cases in which the entire process can take time if the demon is upper-level (such as when Taydeus took a few seconds to explode after he died or when the spell to vanquish Lainey, the queen of the Cicada Demons, was slow causing Macy Vaughn to have to crush her with a control panel).
Rulers of the Underworld
These are the most powerful demons at the top of the demon hierarchy:
Upper-level demons are very powerful demons with high status. These demons usually require the Power of Three to vanquish, and some of them are also impervious, or at least resilient, to physical harm. Despite his power, the Harbinger of Hell was vulnerable to sugar due to his physiology having a high concentration of sulphuric acid, which reacts violently with sugar. Some examples of these demons are:
These are demons with basic powers. They are easier to vanquish and don't usually require the Power of Three. Some don't even require magical means. One Demon had an acid based composition and was destroyed by Sodium Bicarbonate, an alkali substance that neutralises acid. Some examples of these demons are:
- Possessor Demons
- Demon Dogs
- Imposter Demons
- Shadow Demons
- Cicada Demons
- Shokravus Demons (extinct)
- Demon Mammon (only mentioned)
- Abiku Demons
- When vanquished, demonic corpses tend to explode/vanish to prevent demonic existence from being discovered by mortals.
- Most of the more powerful demons have a certain degree of enhanced durability, thereby can survive attacks that normally would be lethal. According to Harry Greenwood in "Touched by a Demon", the common characteristics of most demons include thickened skin with fraying nerves, which contributes to the dulling of their pain receptors.
- This was demonstrated in "Keep Calm and Harry On", when the demon Alastor not only showed no pain after he was stabbed by a knife in his forehead, but he also used it to cut his own face to reveal his demonic form without showing any sign of pain.
- However, it seems that some demons can still feel pain, as Hunter was visibly in pain after he was attacked by the Sarcana's crows in "Jingle Hell". However, this could be because the attack was magical in nature.
- It has been revealed in "Things to Do in Seattle When You're Dead" that demons have at least four different classes, particularly known as "Vagrants", "Malignants", "Carnals", and "Primordials". All of them had been at war against each other and witches for centuries.
- According to Harry, salt can speed up the desiccation of certain demons .