Certain Devilish Enchantments

In this plain there are a number of villages and towns which have lofty walls of mud, made as a defence against the banditti, who are very numerous, and are called CARAONAS. This name is given them because they are the sons of Indian mothers by Tartar fathers. And you must know that when these Caraonas wish to make a plundering incursion, they have certain devilish enchantments whereby they do bring darkness over the face of day, insomuch that you can scarcely discern your comrade riding beside you [...] In this way they extend across the whole plain that they are going to harry, and catch every living thing that is found outside of the towns and villages; man, woman, or beast, nothing can escape them! The old men whom they take in this way they butcher; the young men and the women they sell for slaves in other countries; thus the whole land is ruined, and has become well-nigh a desert. 

- The Travels of Marco Polo, Book 1, Chapter 18

Marco Polo had good reason to take the Caraonas seriously. While he was travelling through Persia, a band of them attacked him and his companions 'in such a darkness as that I have told you of', killing or capturing most of them; he and a few others escaped by pure good fortune, fleeing for refuge into a nearby village. Probably the magical darkness that they were said to be able to conjure was nothing but a habit of using the local dust storms to conceal their movements. But this is fantasy: so why not take Master Marco at his word? 

Thus: the Brigands of the Noonday Dark. A robber-tribe, savage and merciless, living out in the wild lands, descending like thunder upon vulnerable caravans and then fleeing back to hiding places deep in the desert: they attack only under the cover of darkness, but unlike other bandits, when nature fails to provide the darkness they desire they simply conjure up their own. The Brigands know a spell which makes the light fail, until 'you can scarcely discern your comrade riding beside you': this spell, once uttered, affects the land for miles around, and lasts for hours at a time. Travellers know, of course, that this unnatural darkness is a sign that the Brigands are lurking nearby; but they are skilled in riding soundlessly, and even the most alert caravan will be lucky to know which direction they are about to strike from before the Brigands are upon them.

The 'devilish enchantments' of the Brigands of the Noonday Dark are as simple as children's rhymes - which is just as well, given the average level of educational attainment amongst them. However, they will only work for an individual who fulfils two requirements. Firstly, they must be of first-generation mixed ethnicity, with a mother from one ethnic group and a father from a very different one; and, secondly, they must have undergone a process of ritual preparation which the Brigands refer to as 'drinking the sun', in the course of which they must consume appalling quantities of scalding liquids whose exact composition is known only to the chiefs of the Brigands and their most trusted lieutenants. Those who survive this ceremonial ordeal can then call down the darkness at will, turning day into night within a 3d6 mile radius for the next 1d6 hours. Each time they do so they take 1d6 damage, which cannot be healed by any means until the darkness has dispersed. Calling down the darkness twice in the same day increases this damage to 2d6; a third calling causes 3d6 damage, and so on. These 'night-callers' are very valuable to the Brigands, so they will only push them to endanger their own lives through repeatedly calling down the dark in situations of dire necessity.

Within the area affected by the darkness, visibility drops to about 15', which makes missile weapons pretty much useless. The Brigands themselves prefer to use clubs and nets, in the hope of capturing their victims alive and subsequently selling them as slaves. Such is their bad reputation, however, that few 'respectable' slave dealers will have anything to do with them; and, as a result, most of their captives ultimately end up being sold in the slave markets of the Wicked City. They, at least, turn no-one away: and in the choking smog of the Grand Bazaar, under the shadows of the Cobweb, the sunlight-hating Brigands of the Noonday Dark tend to feel right at home. 

If a Brigand night-caller ever comes into skin-to-skin contact with a Child of the Sun, the night-caller will spontaneously combust. The Brigands do not know this to be the case.