With religions and cults in fantasy worlds it's often all too easy to fall into a creative rut whereby you dream up things like this;
"Ariel is Goddess of the Sky. Her holy places are high places and her holy colour is blue. Her priesthood is opposed to erm... earth things and things underground. Things that are sacred to her followers are errr... the sky. And clouds and birds and precipitation. They hate soil and caves."
Real religions are all more quirky with that with some very odd strictures on behaviour. Roll a d20 and add this nonsense to your made-up religion.
1 - Religion practises genital mutilation shortly after birth
2 - Religion has grown out of an earlier, still extant religion worshipping the same deity and has an ambivalent relationship with that earlier religion.
3 - Religion is a schism from another religion and whilst their practises and beliefs are 80-85% identical, enough difference is found to permit a large degree of antipathy
4 - Some observers believe that this religions earliest writings are corrupted oral traditions attributing divine powers and presence to ancient astronauts who have manipulated the development and evolution of creatures upon this world.
5 - Religion follows it's writings literally, but only when translated into one specific language and one printing of it's writings. All others are untrustworthy.
6 - Religion's priesthood are forced into celibacy in order to avoid dynastic ambitions.
7 - Religion holds that's it's spiritual leader is reincarnated after death and accordingly puts much effort into locating the infant into which he has been reborn and elevating him to a position of power.
8 - Religion is monotheistic yet worships a range of minor, intermediary figures.
9 - Religion's objective to idolatry is so extreme that no visual depiction of it's most holy figures are allowed.
10 - Religion practises ritualised cannibalism with a non-meat substitute in an echo of earlier sacrificial practise.
11 - Religion holds that if a mortal is a good member of it's religion it may inherit the mantle of it's deity off an another planet somewhere.
12 - Religion has dietary requirements that seem to be a hangover of earlier civic law.
13 - Religion is entwined with mechanisms of an otherwise non-theocratic state - Monarch is also symbolic head of this religion.
14 - Religion requires that it's male clerics genitals are not misshapen.
15 - Religion is of eschatological nature (End of World is nigh)
16 - Religion allows polygamy in a male dominated culture (or polyandry in the obverse) and may be in conflict with civil authorities over this.
17 - Religion believes in reincarnation and karma with the disabled having been at fault in a previous life.
18 - Religion attempts to keep the contents of it's holy books away from lay worshippers.
19 - Religion has a priesthood divided into levels with cash donations required to advance a level.
20 - Religion's holy writings are held to be parables and fables, not absolute truth.
P.S. I See I What I Did There