For reference, here's a tally of Deities from the Young Kingdoms setting. Apart from these there are a multitude of servants and minor entities, plus lesser Gods and Demons worshiped regionally, some of whom may reside on this Material Plane. Not all beings worshipped as Deities grant spells or powers directly in the AD&D sense, but most will. Some grant only knowledge of sorcery or science, the means on unlocking personal power, or items and servants.
Monotheism is non-existent, most people worship a pantheon, or part of a pantheon, with perhaps a favorite deity accordign to their lifestyle, tradition, culture and education. Monolatrism occurs only among priests and champions of divinities, or those that have taken a specific one as a patron, either individually or by joining an order devote to it.
Atheism as such also does not exist, for the Gods are empirically real, but a rare form of Meta-Apostasy does occur when an individual renounces worship of any deity and responsibility in the Cosmic Conflict to strike out on his own or for humanity's own sake. The maximum exponent of this, of course, are some of the seekers of Tanelorn.
Other types of faiths also exist, ancestor worship, animist, shamanism, mystery cults of self-knowledge, etc; but these all defer to what their adherents know about the Alignments of the Eternal Conflict.
The cult of the Elemental Lords is mostly associated with the lower and working classes (peasants worship Grome, sailors sacrifice to Straasha for calm seas and to Misha for fair winds, smiths pray to Kakatal and Grome, etc) except for Misha who is favored by the elites an nobility due to its association with the skies and elevation.
The cult of the Beast Lords is practically unknown except among some primitives, savages and barbarians (and Melnibonéans too if one accounts the ancient pacts celebrated with these entities).
The cult of the Cosmic Balance does not exist as such, at least not with places of worship and clergy. It is more of a brotherhood of thought and deed which anyone can join. While every other cult ultimately strives for the victory and interests of its faction and worshiped entities, the cult of the Balance holds the greatest variety of attitudes ranging from a "simply don't care" attitude to a pro-active stance on the Eternal Conflict that seeks to maintain the status quo and prevent cosmic imbalances.
Organized cults of Law and Chaos are the purvey of the most civilized and advanced societies of the Young Kingdoms, and have displace the popularity of the Elemental cults as civilization advanced.
None of the groups of deities indicated here acts as a cohesive whole except in the most dire, desperate circumstances. Dislikes, petty hatreds and competition are common among each group and individual divine entities are not above collaborating with another of an opposite faction against one of their own (the current roster and position held are not the original ones, members of pantheons have fallen, been demoted or cast out in the past).
This attitude extends to the faithful and even whole nations. There are no unified Churches beyond the national level, no "Vatican of Chaos", "Pope of Law" or "Council of the Elemental Churches". The soldiers of the Young Kingdoms can go to war with prayers on their lips to the exact same Gods as their foes. If anything, the clashes between two cultures ferociously aligned with the same Cosmic Axis may be more brutal and savage then those between Law and Chaos.
Rather than Alignment alone, nations can be better defined by their levels of tolerance (or lack of it) in these matters. Among the places where one's chosen religion alone may be detrimental to one's health are Melniboné and Pan Tang (whole-sided with Chaos), the Purple Towns and Vilmir (with their inquisitorial attitudes towards magic and Chaos), Dorel (avowed Chaos-haters), Fwem-Omeyo (a Melnibonéan colony which will one day become Dharijor) and certain Chaotic nations of the Unknown East. Everywhere else a traveler is not likely to suffer severe consequences for religious matters. Among the most religiously tolerant nations, which may go as far as having temples of Law and Chaos on the same city are Argimiliar, Filkhar, Pikarayd, Tarkesh and Shazar.
Elemental Deities
Grome Lord of the Earth, King of the Land Below the Roots and Earth Elementals
Kakatal the Fire Lord
Misha Lord of the Wind Giants
Straasha Lord of the Water Elementals
Chaos Lords
Arioch the Duke of Hell, Lord of the Seven Darks, Knight of the Swords, Duke of the Crimson Hells
Artigkern, Drinker of Oceans, Drainer of Worlds
Balaan the Grim-Faced, Lord of Ecstatic Agony and Unbearable Pleasures
Balo the Insane Jester and Minstrel, of neither Chaos nor Law
Chardros the Reaper, Lord of the Graves
Checkalakh the Burning God
Count Mashabak
Eequor the Blue Lady of Dismay, Goddess of Sorrowing Solitude
Hionhurn the Executioner, Lord of the Gallows
Mabelode the Faceless, King of the Swords, Ruler of Shadows
Maluk the Silent Watcher of the Single Eye, Lord of Treachery
Narjhan the Lord of Beggars
Pyaray the Tentacled Whisperer of Impossible Secrets, Lord of the Fleets of Chaos
Slortar the Old
Xiombarg the Sword-Queen, Promiser of Eternal Life
Lords of Law
Arkyn the Meticulous, Lord of Natural Law
Captain Horace Quelch Servant of Great Singularity, Harbinger of Final Order, the Original Insect
Donblas the Justice Maker, Lord of the Law of Righteous Vengeance, the White Lord
Elgis the Gentle, Lord of Harmony
Goldar the Profiteer, Lord of Progress and Wealth
Lady Inald
Miggea The Mad, Duchess of Dolwic
Mirath of the White Hands, Lord of Mortality
Oldreg the Prince of Tidiness
Salik the Potent, Lord of Fertility
Shalod
Theril of the Guiding Hands, Lord of Inspiration
Tovik the Relentless, Lord of Violence
Vallyn the Wise, Lord of Achievement
Beast Lords
Ap-yss-Alara, Lady of Swine, Pigs and Boars
Fileet the Lady of Birds
Haaashastaak, Master of All Lizardkind
Meerclar, Mistress of catkind
Nnuuurrrr'c'c', Master of the Insect Swarm, King with Wings
Nuru-ah, Master of Cattle
Roofdrak, Master of All Dogs, Wolves and Foxes
Etc...
The Grey Lords
Names and number unknown
The Cosmic Balance
