The ultimate manifestation of the demonic arcane on Azeroth is fel (aka fel energy or fel magic). This energy, which most commonly manifests itself as ghastly, green-yellow flame, is arcane magic at its most corrupt, for it employs the blood of demons. Spells with the fel discriptor are very difficult to resist. Casting a fel spell is described by many spellcasters as a euphoric experience. If arcane magic is an addiction, fel magic is the embodiment of the drug in its purest form.
When the demons brought death and damnation to Azeroth, they also carried their own brand of magic to the world. Fel magic is pure, evil and arcane; it resides in the blood of demons. This blood has magical properties; it addicts arcane magic users and can be used to create evil weapons. When a weapon is forged in demon blood, it becomes a fel weapon. It glows with a foul, yellow-green fire and deals extra damage to good-aligned opponents. Some arcanists can cast fel spells, perhaps after drinking demon blood.
Since the Burning Legion returned to Azeroth, the world's heroes have encountered fel weapons and fel magic at an increasing frequency. As demon cults continue to fester and grow in Desolace, Ashenvale Forest, and other remote corners, gruesome sacrifices are held to entice demons into giving their blood in trade. The cultists use their blood to enchant the weapons that they hope will bring about their masters' ultimate victory.
Unlike arcane magic the use of fel magic corrupts the user’s body and soul. By contrast the chief danger of arcane magic is that using it inevitably leads to the desire to wield greater power: power that only fel magic can provide.
Demons sometimes tempt spellcasters by offering small amounts of their blood in exchange for services. If the recipient drinks the demon's blood within 24 hours of the offering, the next arcane spell he casts will be a fel spell. Fel blood is highly addictive as well as corruptive. Anyone who drinks it has a chance of becoming dependent on fel blood, and unless the person continues to drink it daily, he will suffer withdrawal symptoms. He has a chance of breaking the addiction seven days after first drinking the fel blood.
Fel-poisoned creatures are another threat from the Twisting Nether. They are starting to appear in places where the Burning Legion is strongest. When a creature with a natural poison attack is imbued with fel energy, its venom becomes more difficult to resist.
Grammar and usage
Fel is a prefix usually associated with demonology, or more specifically, the Burning Legion. The word itself has no singular meaning (that has been explained at least), but is usually affixed to other words to denote their corruptive nature or connection to demonology.
The game refers at least once to Fel in a singular meaning. An Undercity quest has in its description sentence, "There, slimes are found all around pools of water blessed by the touch of Fel.", so there may in fact be a singular meaning.
A second reference to Fel in singular form is found in the quest in which it is said, "The satyrs have been able to corrupt anything they come in contact with, which includes the ancients that made Felwood their home. By the use of the fel, the spirit of the ancient has been bound and tortured, never completely released. The felbind you found is no doubt related." Furthermore, Eridan Bluewind in the Emerald Sanctuary states "... Although the land is named for the very thing that corrupted it..." These references would seem to suggest that fel is indeed some substance, force, or energy. Though, perhaps, it could also refer to a technique or the corrupting influence of the Burning Legion or even demon blood.
Having an innate association with demonology, warlocks have adopted a connection to the darkest fel energies. Through their understandings of demonology they are able to dominate certain agents of the Burning Legion, such as imps, voidwalkers, succubi, felhounds, and felguards, and through their enslave demon ability, doomguards, infernals, and gan'arg demons as well.
In Hebrew, the word "אפל" (Afel) means "dark" or "tainted". The English adjective "fell" means "cruel" or "savage". The word "fel" can also mean "bile", and according to The American Heritage® Dictionary of the English Language: Fourth Edition (2000), it is related to a number of words of Indo-European origin: yellow, gold, gall, cholera, and felon, to mention a few. The same source indicates that the Indo-European root from which it is derived, ghel, meant "to shine". It may also find it's origin in the Old-English word "fūl" which means "foul" and is the origin of the word "defile". Fel also is a Swedish word for "Wrong" or "Incorrect", it is however pronounced differently (the E is pronounced as the first E of "Error" which make the word sound like "fEl").
- Felwood: The formerly beautiful forest adjacent to Ashenvale that has since been corrupted by demons and made into a tainted cesspool.
- The Fel Pits: The scalding pools lining the western edge of the Hand of Gul'dan in central Shadowmoon Valley.
- Fel orc: The derivative of the orc race that resulted from their blood pact with the Burning Legion and their consumption of the Blood of Mannoroth.
- Felguard: The basic foot soldiers of the Legion.
- Felhound: Guardians and pets of the pit lords of the Burning Legion, used to sniff out sources of magic.
- Felsteed: A demonic mount available for summoning by warlocks.
- Felcloth: A tainted fabric woven by demonic energies which can be purified by tailors to create Mooncloth. It drops off demons.
- Felheart Raiment: A warlock armor set.
- Felboar: A demonic pig.
- Fel dragon: A demonic dragon. Notable one is Felmyst
- Fel reaver: Legion mechanical monster.
- Felblood elf, aka Fel elf: blood elves loyal to Kael'thas Sunstrider who have been granted demonic power.