The game word of the Iron Kingdoms includes a pantheon that is in some ways unusual for a Dungeons & Dragons high fantasy environment. This is no great suprise, as the Iron Kingdoms is a significantly unusual D&D campaign setting.
In the similarities column, you’ve got some old standbys: Dwarves and Elves have separate pantheons and religious traditions entirely. The Dwarves revere the literal founders of their race, the Stone Fathers, which the Elves have their own mysterious religious tradition (they don’t like to talk about it).
Humans have yet another pantheon, unrelated to the Elves and Dwarves (we’re still in “similar to other campaigns” mode here). The uncivilized humanoids of the world have yet another religious tradition, and there is your obligatory Dragon Cult.
But all of this gets a little turned around. The Humans only have four Gods to speak of, one of whom is so old as to be largely irrelevant in most Human territories (Menoth, the Lawgiver of the Old Religion), and another so new and mysterious as to be utterly unknown by most layfolks (Cyriss, Maiden of the Gears). Instead of fleshing out the entire alignment wheel (a Lawful Good, Lawful Evil, Lawful Good, Neutral Good, Neutral, Neutral Evil, Chaotic Good, Chaotic Neutral, and Chaotic Evil God) or placing a horde of specialist deities governing overlapping or otherwise redundant porfolios (think Chauntea, Meilikki, and Silvanus from Forgotten Realms) or a ensuring there be a Deity for each alignment, the humans of West Immoren primarily worship a single God, Morrow. A small number of folks secretly worship Thamar, Morrow’s evil sister.
The human deities cover four alignments (Lawful Neutral, Neutral Good, Neutral, and Neutral Evil). Each God is well described and has its own tradition (Thamar and Morrow were twins before ascending, so their myths have a great deal of common ground). Each God has its own kind of following. The Twins Morrow and Menoth even have their own Saint-like underlings (ascendants and scions, respectively) that have their own spheres of influence but are entirely subordinant to the proper Gods.
The odd-man out is the female Cyriss, whose sphere of influence is found in the laws of mathematics and mechanics. She has a small but devout following spread out wherever the learned can be found. They construct great devices for unfathomable purposes. Cyriss is not particular about good and evil, nor even law and chaos. Her followers may become great allies or fearsome enemies for any of the Kingdoms. This remains to be seen, as they have no major temples in the capitols of Caspia, Khador, Llael, or Ord.
The uncivilized folks of the world (or least recently civilized) have strong ties to two very old Gods, the Devourer Wurm and Dhunia. These folks include the Trolls and Trollkin, Ogrun, Gobbers, and Bogrun. The Wurm is a chaotic, destructive beast and perpetual foe of Menoth. Dhunia is a earth-mother figure that keeps the world fertile and the cycle of renewal running along normally.
Wurm cultists have a deservedly bad rap for human sacrifice and wanton, reckless destruction. Dhunia is the primary deity of the more settled, civilized non-humans of the Iron Kingdoms. Your average Gobber working as a Junker on the Khador/Cygnar border is likely a follower of Dhunia, if only a casual one. Wurm Cultists have a tendency to have problems with orderly transactions like… Bartering over scrap.
This relative paucity of religions in this campaign setting has a number of probable repercussions unusual for a D&D adventuring party. Players are accustomed to a great deal of religious diversity amongst their ranks. It is not uncommon for every member of a 5-member party to worship 5 different Gods and not think twice about it. This isn’t so in the IK.
The vast majority of Humans worship Morrow. While this noble and good deity has no necessary conflict with Menoth, the strict but fair God of the old religion, there has been a streak of religious war in the past 100 years. An entire chunk of Cygnar has effectively ceded from the rest of the country as a theocratic protectorate. During the civil war that split Cygnar in two, most followers of Menoth relocated to the Southeast corner of the land, and all followers of Morrow have left that area or converted in the years since, in the face of severe religious laws outlawing their faith.
The result is that your average Cygnaran doesn’t trust a Cleric of Menoth further than he can kick him. A Cleric of Menoth from the Protectorate is highly unlikely to tolerate displays of dedication to Morrow in his presence. Only very unusual circumstances would lead a Protectorate Cleric to adventure with a Cleric of another faith (or Paladin or Monk, for that matter).
Similarly, as every area other than Cryx is predominantly goodly in population. They are uncomfortable with an generally opposed to Thamar worship entirely, so any player character with Thamar and/or one of her scions had better keep it firmly under his hat. There are no large population centers that are Evil Goddess-friendly, and she has no major temples where any mortal army is likely to find them.
Prejudices regarding the past behaviors of depraved barbarians lead by Wurm-cultists throughout history would lead to similar problems for any player that wants to play an enlightened-but-free-spirited Trollkin priest of the Wurm adventuring in the Iron Kingdoms. However, at least they would be able to find gobber, trollkin, and ogrun population centers scattered about, where he wouldn’t be likely to put him to the stake.
Additionally, the laity have some game-mechanic encouragements to actively maintain the practice of their faith. Each Ascendant of Morrow and Scion of Thamar grants bonuses not just to the clergy, but also to lay folk. This is a reward system that is built into the campaign setting so that DMs can dole out a little extra loving to players that have their characters earnestly pursue the worship of their patrons and Gods. Compare this to the “benefits” of having a patron God in the Forgotten Realms. There all you get is to bypass judgement at the feet of Kelemvor. In the Iron Kingdoms, faith pays now, not later.
One of the players in my current campaign has been toying with the idea of running an Iron Kingdoms campaign, and I have lent him my copy of their Character Primer supplement to help him get a feel for this rather excellent setting. For more information about the religions of the IK, please see their Deities of the Iron Kingdoms and the Lock & Load Character Primer, available at discerning hobbyist and book stores.