Weirdest plausible religions

But cult of holy fire is rather little adaptable to Mosaic-Christian conception of this element, where it is associated with hell and punishment.

On the other hand, the burning bush is god manifesting through sacred fire isn't it?
Also, any attempt to map the Christian trinity onto the triad of Zoroastrian gods would be interesting. The Son/Jesus as Mithra, The Father as Ahura Mazda, the Holy Spirit as Anahita(perhaps with close traditional associations between churches and rivers/wells, given Anahita's role as guardian of waters, or given my understanding of Zoroastrianism a requirement that all masses must be conducted in the presence of fresh pure water and consecrated fire)?
 
On the other hand, the burning bush is god manifesting through sacred fire isn't it?
Also, any attempt to map the Christian trinity onto the triad of Zoroastrian gods would be interesting. The Son/Jesus as Mithra, The Father as Ahura Mazda, the Holy Spirit as Anahita(perhaps with close traditional associations between churches and rivers/wells, given Anahita's role as guardian of waters, or given my understanding of Zoroastrianism a requirement that all masses must be conducted in the presence of fresh pure water and consecrated fire)?

With ritual baptism in water then dried by fire
Or perhaps baptism in water and oil which is then burned.
 
After a somewhat different conquest and colonization of the Aztecs by the Spaniards (or any other European empire), which results in a much less severe decline, the population is gradually made to adopt Christianity, but the missionaries are unable to enforce correct interpretations of the dogma over a long period of time, and the colonial administration is busy with other problems and endeavors. It evolves into a very local flavor of Christianity, blended and overlapping with Aztec paganism in many ways.

The people worship "The God" and many Saints, but some of the small statues and idols commonly made of them look really weird, and there are many rituals and folk traditions no scholar of the bible could explain. On Christmas, the people celebrate, hang images of crosses all over their houses and in the streets. They make multiple man-shaped cakes from bread, honey and nuts, and at the end of the day cut them up and give pieces of this "body of Christ" to any guests or passersby.

Nobody is really sure what happens at Easter; the traditions seem to vary from village to village, although one common element is having people visit their friends and neighbors, dressed in animal skins, waving about crosses, and shouting "Merry Christmas!" as loudly as possible.

Parents often dress their children up in feathers and small makeshift uniforms before baptism - a questionable practice, but too harmless to be bothered with and if the priest makes a fuss they often perform a second, secret baptism themselves.
Like baptisms, burials are outwardly Christian, but still accompanied by many auxiliary rituals and superstitions. The dead are sometimes buried with a wooden cross in one hand and a shovel in the other one, presumably to dig themselves out on the hour of the Resurrection.

There are also whispers of darker traditions going on in isolated communities and remote settlements, where the colonial regime only occasionally comes to visit. Allegedly, when the crops failed, a child from the village was sacrificed to appease Saint Elijah; sometimes, it's an animal. And in the first days of December, they allegedly reenacted the betrayal of Christ by Judas and his subsequent crucifixion, with very real nails and crosses. According to some, these traditions continued underground as late as the 18th century, when they were finally driven out of existence or evolved into minor rituals simulated with objects rather then people.
 
the reenactment of Christ's crucifixion was practiced regularly in the provinces here until recently. just saying.

so, yeah. OTL Christianity still fits the bill. especially folk Christianity.
 
Luciferism, from an alternate reading of Genesis (I know a minor Abrahamanic religion follows quite a similar creed, but can't remember its name at the moment). Based on the idea that, since Humans differ from animals by their intelligence and their soul, intelligence is the manifestation of the soul. Now as initially created Humans were unintelligent, explicitly 'like animals' and thus soulless: Humankind received its soul not from its original creator but from a Promethean character Lucifer 'the Light Bringer'. Not at all 'satanism' / 'Abrahamanism in negative', there is no opposition, no 'revolt', only a two-steps creation even without a bloody episode like the murder of Uranus or Ymir. Thus not a specially weird religion, the main difference with OTL Abrahamanic ones being the absence of 'original sin' and of the associated permanent need of atonement and search for redemption. Another difference would be that, given her role in the 'positive' Apple Incident Eve (perhaps known as Lilith?) would be perceived as the ultimate heroine of Humankind and the First High Priestess rather than as the Agent of Satan, the Temptatrix culprit of the original sin. This would perhaps lead to a clergy dominated by women if not entirely female, anyway to a more gynophilous, less misogynous society.

Triadism: popular Catholicism evolved to polytheism, with the biological triad Father - Mother - Son (not dissimilar to the Osiris - Isis - Horus one, but without the murder and odd resurrection of the Father) at the head of a pantheon of Saints. Polytheism being generally open, newly encountered deities, once renamed Saints (such as the Aztec Santa Muerte and the African Saints of the Santeria) would be part of the official pantheon.

Maryamism: Mary raised to preeminence to the level of a hedonitheist / quasi-monotheist Mother Goddess. Being already the Virgin and the Mother she would just lack a '2nd function' aspect to become a Triple Goddess; probably not a fully 'warrior' aspect, but a form of association with (heroic) death à la Badb Catha / Valfreya, or with the Underworld: far from impossible, Villon already called her 'Souveraine des infernaux paluds'.

Apocalyptism: the cult of the Four Horsemen, devoted to trigger their coming and that of the end of times.
 
Luciferism, from an alternate reading of Genesis (I know a minor Abrahamanic religion follows quite a similar creed, but can't remember its name at the moment)
Are you thinking of the Yezdis? They revere the archangel Melek Taus, who refused to bow down to Adam and was rewarded for his refusal and who is also known as Shaitan, leading to some non-Yezdis thinking Yezdis were satan-worshippers.
 
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