Demons

Demons are a race of magical beings motivated by Evil. They seek out to kill innocents and the forces of Good. Demons are unable to feel emotions and possess no soul or conscience. Almost all demons are immortal, and in some occasions, however, a demon can become good and desire to live a mortal life.

For centuries they have been ruled by the Source of All Evil, who claimed to be the most powerful of all demons. Most demons live in the Underworld or the mortal world, depending on what goal they wish to achieve or how they influence the mortal world. When exiled, a demon is not allowed to live in or enter the Underworld which is punishable by death.

Demons are said to come in every shape and form. And while that is true, most demons seem to have a human appearance, either by nature or with magical help. It is also possible for demon to have an amorphous body instead of physical form.

Low-level demons are easily vanquishable with powers, a basic potion, or a spell. Upper-level demons require Power of Three spells and potions.

The Demon Hierarchy
There is a hierarchy set out in the Underworld that defines the rank of all demonkind and those evils who are beneath them. Depending on the hierarchy, demons are usually classified into two groups: lower-level andupper-level.

At the top of the demonic hierarchy are the upper-level demons and those who rule the Underworld. At the bottom are those demons who were banished from the Underworld and thus live in exile and Warlocks.

Only a select few exist outside the basic structure of the demonic hierarchy: The Tribunal and the advisers of evil (Seers, Dark Priestesses, Oracles). They act as a neutral party.

Powers
There are many powers, some which are generally possessed by many demons, others which are unique to their owners.

Lower-level demons generally have basic demonic powers that are of not much use. Upper-level demons generally possess the ability to shimmer and throw energy balls, and depending on their status can throw Fireballs as well. The Source of All Evil was the one of the only demons to be able to teleport with flames, a way to show of his high status and leadership.

However, demons can collect various powers by killing other demons or stealing them, making them much more powerful. Demons like Zankou and Zahn in particular were able to do so. Zahn was able to up his rank from low- to upper-level over the centuries.

Most demons are not able to cast spells and brew potions but are vulnerable to them. Upper-level demons might have learned to master these abilities or at least grow strong enough to withstand them or become immune. Members of the Ordo Malorum for example are immune to the powers of witches.

Book of Shadows
The Halliwell Book of Shadows contains specific entries on countless demons, often telling them what these demons wish to achieve and how they can be vanquished. Demons who do not have an entry in the Book of Shadows are usually low-level and too insignificant to mention. Besides these entries, the Book of Shadows contains a general entry on demons as well.
 *  Demons 
 * Observations upon the
 * Nature, the Number, and the
 * Operations of the Devils.

Notes & Trivia

 * Humans can be converted to demons (through a special academy) and vice versa (with the help of a Sorcerer or the Elders).
 * According to Cole Turner, upper-level demons, especially those with a human-half, bleed red and low-level demons bleed green.