The original In Darkest Warrens system has no specific religious system, though the "monsters" include angels, devils, and demons.
In Nezrak's world, there are three known religions. Nezrak and his followers worship Yervaar, a very powerful evil god or demon who gives Nezrak and his minions power in return for human sacrifices.
His Barbarian allies have their own pantheon, a distorted form of a Norse/Germanic type of tradition, as follows:

Gods of the Barbarians:
Tolvar the Tormented: Pain is the price of wisdom. He was hanged and pierced with a spear to win wisdom. He is worshipped chiefly by warlocks. His sacrifices are hanged men.
Vod the Slayer: God of war: honor is won only by war; worshipped by male barbarians and by some warriors of the Foe side, who are often half-orcs. His sacrifices are the heads of men taken in battle, especially champions of the free side.
Limmodh: Lord of Lightning. Master of stormy skies. He is worshipped by male barbarians and some treasure-hunters, thieves and rogues, for he is a god of smiths as well as warriors. His sacrifices are men with the blood eagle carved on their backs.
Greyfa consort of Torvar, mother of sorr0ws, goddess of crones, women dying in chlidbirth, children stillborn or dying young, giver of poison and other dangerous knowledge. Worshipped by female warlocks and mages on the side of the foe. Her sacrifices are women drowned or poisoned.
Vizhla Consort of Limmodh, the warweaver, inciter of quarrels, who weaves the fate of wars on the loom strung with the guts of men, also goddess of the beauty that maddens, inciting lust, jealousy and ravishment of captives. Her maidens carry the souls of dead champions to join the eternally warring warbands of Vod and Limmodh (and herself). Worshipped by barbarian women, especially warriors. Her sacrifices are limbs or private parts of slain male warriors.
Note: The Gods of the Barbarians became much darker figures after Nezrak’s God remade the world. Before the catastrophe, they were kinder, sometimes stern but always just. Torval was god of men’s wisdom, Vod of honorable war, Limmodh of smiths, Greyfa of women’s wisdom, Vizhla of love.

The Free Peoples (elves, dwarves, halflings and good humans) have their own pantheon loosely modeled on the classical Greco-Roman one, but very simplified.

Gods of the Free Peoples:
Halbol Lord of the Forest, worshipped chiefly by the elves and by some human rangers and free barbarians in the Freewood. Offerings: nuts, fruits, and well-carved wood.
Nelgul: Lord of Roads, god of merchants, rogues, treasure-hunters, mages and others who live by their wits. Offerings: coins (usually given to charity), skillfully worked metals, jewels and shares of plunder gained by wit rather than force.
Yalsol: Lord of the Battlefield worshipped by warriors, some rangers, and some barbarians who have turned to the free side. Offerings: trophies of honorably won weapons and armor, especially those taken from champions of the foe.
Meboz: Lord of the Sea worshipped by seagoing merchants and sailors of the naval patrols which protect the isles and their sea-bourne commerce from the sea-reavers and corsairs. Offerings: fish and other sea creatures, pearls, coral and other sea jewels, also trophies taken in honorable naval war, especially the rams of galleys.
Gumoma, Lady of the Fields, plant, animal and human fertility. Worshipped by farmers and by women. Offerings: grains, raw or baked, grapes and other cultivated plants, wine and beer, honey and mead, also meats which are then shared at feasts.
Tyayima: Lady of the Hunt and of wild animals. Worshipped by some rangers and young women, especially women who choose to go out as warriors or rangers.  Offerings: venison and other meats taken in the hunt, furs, hides and leathers.
Halgoz Gylyoz: The High God above all gods is said to be the ultimate Maker and Ruler of the World, but this God rarely intervenes in the affairs of mortals. Very few people actually follow him as their personal god.

Following the implied system in the original rules, it might be possible to have a strictly dualistic Yervaar vs. Halgoz  (Satan vs. God)system, but that is not how I have designed this campaign.
This message was last edited by the GM at 02:36, Tue 23 Jan.