The Church of Mathus is the newly appointed state religion of the empire of Arden, established by King Gerard Montaigne in an effort to further submit his conquered realms and to diminish the Fellisian religion of the Maker as witchcraft. This is also a convenient tool to persecute remaining wizards in the flatlands.
Devotees follow The Book of Malthus, the sacred text, and their mission is to rid the world of sorcery. The Darian Guild are mage hunters, thirsty for literally drinking the blood of wizards. They seek out a mage target, do away with their amulets, place a Darian stone of their chests that absorbs all the wizards remaining flash, while also paralyzing get them. They then begin a ritual of sacrifice, making a gouge in the wizard's arm and letting them bleed out while the member of the guild drink the blood.
Malthus friars are also in charge of the kingdom's registry, documenting every birth, class not withstanding.