The Touch of Darkness

By definition, a practitioner of Black Magic is someone who specialises in the casting of offensive, aggressive and destructive spells. Black magic centres around the theory that "the best defence is a good offence" and thus concentrates on the use of magics that are meant solely for the purpose of destroying. To this end, the Black Magician must learn the arts of many different caster types, picking and choosing which spells to keep and which spells to discard. Also, as with all distinct caster types, Black Mages (the term used for a practitioner of Black Magic, despite the fact that they are not true mages, but are rather only mages by the etymological definition of the word (i.e. a Magician)) have a few spells specifically of their own.
The Black Mage's spells (remember, these are not real Mages) come from a variety of what might be loosely termed, "The Casting Arts". Though there are a lot of religions which use magic in one form or another, the Black Mage's arsenal comes from the casting arts which are listed here, in The Library of Knowledge. Having an affinity for destructive spells, the Black Mage hones only those spells which bring about the decay or destruction of their target, believing that this is the only useful way to progress in life and magic. Unlike a Sorcerer, the Black Magician may worship certain deities (perhaps even themself, as the Satanist does), and may hold to certain rules of casting which they find improve their performance.
To the end of a well-rounded repertoire of offensive spells, the Black Mage takes from the following arts:
• Conjuring/Demonomancy
• Elemental Magic
• Enchanting
• Necromancy
The use of each of these arts will be further expounded on. As for Conjuring and Demonmancy: these arts tend to found the knowledge base and insidious powers of a Black Mage. Though not used very often for the purpose of totally destroying an enemy, it is quite common in this art to use them for intelligence gathering or for acts of treachery and subtle destruction. Demons, as opposed to standard spells, have intelligence and power that can work in a multitude of ways and can change methods without direct instruction from the caster. Having this benefit, sometimes a demon is the only force necessary to rectify a situation.
Demons, however (and thankfully), are not the only source of power for a Black Mage. One of the landmark abilities of a Black Mage is to be able to take different spells from different casting types altogether, and bind them into one cohering magic form. Another one of the arts that is sapped of it's unique abilities is Elemental magic. Black Mages tend to be fiercely fond of using the Elemental class of magic since it represents the quickest and most effective form of physical destruction available. Fire, among the four elements, is a classic among these casters. Though never able to reach a level of control over the elements that compares with a dedicated Elemental magician, some Black Mages study hard enough that they are eventually able to use the rudimentary level spells of Elemental Magic. With the exception of Earth, the elements are usually mastered at the most basic level by a Black Mage simply for the purpose of being able to use them for unleashing chaos.
Very little from Elemental magic is accessible to a Black Mage, but often, instead of Elemental magic, Enchanting is used. Also with Enchanting, very little is available without dedicated study, but it tends to be far more forgiving and accessible to other caster types. Black Mages use this to enhance their normal operations. If a Black Mage were simply trying to curse someone, this would be the art of choice. Using a Fire Elemental, the conjuration instructions of which can be found at Spirit Online, a Black Mage can create a "spirit" to go and harrass/destroy/harm a selected target (although the Spirit Online link is White magic based, so it will never recommend that you use an Elemental Servant for such purposes). This type of magic is based in Enchanting and will probably not be the strongest ability of a Black Mage, but still is a casting ability worth mentioning.
The final borrowed source of a Black Mage's ability is based in the use of Necromancy. Necromancy is infamous for two things: raising undead minions and vampiric spells. Though the raising of bodies or entities is an ability far above a Black Mage, they are capable of tapping the vampiric and draining powers of Necromancy. By learning the basics of the use of Death Essence, the Black Mage can employ draining spells and spells of harm that will take the magical and/or life energies of a target and add it to one's own reserves (this does not mean that a Black Mage can steal your soul or shorten your life, but rather that a feeling of weariness and lethargy can be induced).
Also, as with every distinct caster type, there are a few spells available to a Black magician that are truly and uniquely for that caster class alone. Much like the Death Essence of Necromancy, Black magic holds power through the use of the black channels. Many Black Mages hold the claim that, much like death essence, there is a black energy source out there that can be commanded and controlled with will power. This enables a variety of spells for the Black Mage. The different uses of the black energy cannot be discussed here in any meaningful way, but knowledge of it's existence forms a base for the Black Mage's studies.
This is the art of the Black Mage: triumph through force.