Doomsayer

A doomsayer is a madman who has been touched by the void. There has been some study into their origins and methods, but such research is very dangerous and many sages and scholars underestimate the power of such study.

One sage managed to become a doomsayer himself, but shortly after was executed by a machine of his own devising as a fail safe. His research noted several key things about the doomsayers and their power: These spells function more like an infection than an arcane invocation, and it infects the emotional state of its targets. Some of the doomsayer's foes have known to be cursed in ways that no remove curse spell can cure after exposure to a doomsayer, even after having killed the offending doomsayer himself.
 * 1) There is a language learned by those 'touched by the void' this is typically warlocks but can be anyone who is unlucky enough to be chosen by the great old ones.
 * 2) The language is impossible for humans to speak fluently, but some words need to be be used in combination with a language that the doomsayer's foe can understand.
 * 3) The words cannot function unless powerful emotions are behind them when spoken.  Emotions like despair, fear and desperation are thought to be the most potent, and tone and volume seem to be a factor as well.
 * 4) Men who know these words must be driven mad by them, otherwise they words would hold no power without their constant state of damnation.