Grand Warlock Nethekurse was a warlock who got his practices from Gul'dan and Teron'gor.
Nethekurse, once a shaman of the Shadowmoon clan, abandoned his reverence for the elements to master the art of wielding fel magic. The demonic energies at his command have left him a husk who finds delight only in torturing young fel orcs to test the limits of their mental and physical strength.
Nethekurse's Dark Practices
Death, Decay, and Destruction
"Run, coward, run!" - After Netherkurse casts Death Coil
Death, in the form of necromantic magic, pushes everything towards a state of entropic decay (or fel decay) and eventual oblivion. Entropy, as it can be defined, is the representation of the unavailability of a system's energy for conversion into work, often interpreted as the degree of disorder. Order, in reality, is most commonly perceived as arcane magic, which necromancy is a school of. However, this does not mean order is always perceived as arcane magic in reality. This type of energy is innately volatile, and wielding it requires intense precision and concentration. Now, conversely, disorder is manifested as highly destructive fel magic, a brutal and extremely addictive energy fueled by drawing life from living beings.
Nethekurse's fel energy is essentially death energy (a necrotic power) according to Chris Metzen and would (or does) — as a destructive force — destroy structures, breaking them down over time or outright obliterating them. Despite that fact, Micky Neilson — veteran of Blizzard Entertainment — stated that fel magic is not the same as death. Fel is the primal force of chaos and it can pool into a green goop when it's in physical form. It is a substance that can be animated (is that substance alive when animate?). Prior to being animated, fel is inanimate and so Nethekurse was, presumably, an animancer or necromancer who was able to animate — or fuel — the fel by drawing life from living beings.
By their very nature, demons are leeches on the living universe—but Nethekurse mastered harnessing the energy of these malefic beings on the field of battle. Nethekurse harvested the souls of his defeated enemies; those specialized in the ways of demonology use this life essence to tap into the Void, pulling all manner of abomination from the chaos of the Twisting Nether. While such a practice is often considered by outsiders to be wicked and reckless, the demonologist maintained absolute control over the summoned creatures. These malignant entities were fully beholden to—and empowered by—the will of the warlock, until banished to the realm from whence they came.
"Your pain amuses me!" - After Netherkurse casts Shadow Sear
Nethekurse, if he was an affliction warlock, was a master of shadow-touched powers, but unlike shadow priests—deadliest when pushed to the brink of insanity—this warlock would have delighted in using fel forces to cause intense pain and suffering in others. He would have reveled in corrupting minds and agonizing souls, leaving enemies in a state of torment that would see them undone in due time.