Easy Access Polytheism, plus an old incomplete pantheon

This is something I've done in settings with polytheistic pantheons where pretty much everyone attempts to get on the good sides of the gods.

Anyone can cast cleric spells! Hooray! However, you don't automatically get spells- you pay for them with Favor, and don't have 100% certainty of what will happen. You get favor by doing things that specific gods like. Donating 1000 coins, a magic item, or other things of great value to one of their temples or doing a quest for the church is a solid way to get a favor point with most gods, as is converting more people to the religion.

Each point of favor is the equivalent to a spell level. Invoking a miracle involves praying for divine intervention. Make a WIS check or a saving throw or something, maybe with a -1 per spell level of the miracle you're praying for. Maybe you have to roll under Favor-Requested Spell Level if you want it to be hard. Anyway, if it works, burn favor and the gods will bestow an appropriate cleric spell of a level up to the amount of favor burned in response to your request, assuming your request is in-line with their goals. If it fails, you can keep praying for a cumulative +1 bonus per consecutive round spent praying.
NOTE: To prevent this from being an exercise in 'mother may I' with the GM, god motives and methods should be pretty obvious, not super sophisticated character studies , and as usual, saying 'yes' will almost always make for a better game than saying 'no'

If something dreadful would happen to you and you have some banked favor, the god you have the highest favor with has a favor-in-20 chance of them attempting to save your bacon independently, though they'll be the ones choosing how much favor to burn(all of it, typically) and what exactly to do with it in that case. They might just blow favor at a 1-1 ratio to increase your saving throw vs getting owned or similar simple mathematical tweaks in your favor if they don't have any truly appropriate spells to save you.

Doing things they don't like will likely incur loss of favor, and doing things they REALLY don't like will result in Wrath- the turning of any positive favor to negative.  Negative favor is similar to positive favor given to your enemies, to be used against you at inopportune moments.


Anyway, here are some examples from my last campaign. The might be bad examples to steal wholesale because there's a bunch of setting-specific divine politics implied, but having factional conflict and conditional alliances and so on makes religion interesting.

you get angels of Riikhus &Mokkhus, cuz Riikhus is just the sun and Mokkhus is just a big goffik dude

Riikhus- The King in the Sun, the Flames Of War Which Purify All, The Unconquered Light
Mokkhus- Counter of Bones, Gatekeeper of the Dead, The Unmoved
+1 Favor- Smite an undead or demonic creature of more HD than yourself, or an enemy priest
+??? Favor- Subjugate a divine spirit and add them to the slave pantheon of the Brothers
-1 Favor- Gain more favor with a slave god than your current total with the Brothers
-1 Favor- Act against the interests of the Church
Wrath- Intentionally gain favor with M'shesh or Lumar
Common Miracles
Riikhus's Trumpet- Garb allies and self in arms and armor in fanfare of light and angelic wingbeats
Wrath of Riikhus- As Inflict Light Wounds but Holy Fire damage, or in sunlight, as Magic Missile
Underworld Manacle- Strip immunity to nonmagical weapons from one undead.
Ancestor Spirit- As Animate dead, but animated dead are lawful faithful of Mokhus and will return to the underworld after their task
Intervention- Angel dispatched to smite evil or spirit the faithful away to safety.

Slave Gods/Saints of the Brothers Riikhus and Mokkhus
Lady of Gardens- Law, Plants, Domesticity, Society
+1 Favor- slay monsters and mutants
+1 Favor- officiate lawful proceedings such as marriage, peace contracts, etc.
-1 Favor- polymorph, mutate, sow chaos, minor crimes
Wrath- Intentional polymorph, mutation, seriously destabilizing crime
Common Miracle- Entangle, Grow Plants

Jackal God Of Yuba
+1 Favor- Eat the warm hearts of your slain foes. +2 if higher HD, +3 if over double HD.
+1 favor- Save a Canine from peril
Common Miracles- Charm Canine, Scare Animal, Curse: Lycanthropy.

Hefon- Goddess of Bonds
+1 Favor- save a friend or family from certain death
+1 Favor- avenge a wrong done to your kin or ally
-1 Favor-Abandon allies in need
Wrath- Betray blood or bondsman
Common miracle- bless, healing, or reversed spells when pursuing vengeance

M'shesh is a nice goddess if you agree death was a stupid idea and a world of zombies would be better
No pain! No need to kill living creatures to eat! Stable population!

Free Gods
M'shesh- Mother of Undead, She-Who-Bars-The-Way, the Black Wind
M'shesh opposes death and pain and will never grant a spell that inflicts harm.
+1 Favor- Spare your enemies rather than slay them this session. Also, kill nothing to eat.
+1 Favor- Convert or slay a priest of Mokkhus or Riikhus- those who do not oppose death are welcome to it!
-1 Favor- Slay fleeing or surrendered foes, or kill without necessity.
Commonest Miracle- Breathe a dead soul of a M'shesh faithful into a corpse, creating an intelligent zombie hireling or raising a faithful player as undead. Immune to poison, discomfort, disease, but still vulnerable to level drain and feel like they need to breathe and eat and sleep. If they don't, they start going crazy. Also zombie PCs break a lot of inherent assumptions about the game, like food, need to breathe, etc etc, and you should be careful with this at low levels.

You can't comprehend Yg's true majesty because you're not a snake
But if you were this image would be majestic indeed

Mother Yg- She-of-Skins, the Long Librarian, Egg-Keeper, Serpentine Matron
+1 Favor- Complete a task for a snake
+1 Favor- Retrieve knowledge unknown even to her
+1 Favor- Consecrate a monster egg to be born as a monster snake instead
-1 Abandon a snake in mortal peril
Wrath- intentionally harm a snake

Common Miracles- cure poison, sticks to snakes. Snakify Egg, cause poison, speak with snake(but never charm snake, you can hire them as hirelings for the usual half share of gold. It is a mystery what they do with it.)
Getting Raise Dead'd makes you a bit more snakey each time.

This is what carved wooden idols of T'liki look like. Only even more annoying.

T'liki- Coinflipper, Shuffler of Souls, The All-(f)or-Nothing
+1 Favor- gamble your most prized possession as an offering to T'liki with 50/50 odds. If you can fool T'liki, you might be able to fake sacrificing it.
+1 Do something risky and stupid, and pull it off. Adventurers can rack favor up pretty quick...
-1 Be boring. Festivals of masks and wanton revelry are held to amuse T'liki and ward off his attempts to 'spice up' peoples lives.


Common Miracles- as a chaotic trickster god, T'liki grants random spells of illusion and confusion.
T'liki can be called to intervene directly with no loss of favor by drawing from a deck of cards, rolling a die, or similar, but his intervention leans towards making situations more chaotic and random, rather than any reliable aid. Certain players will take great joy in having T'liki be blamed for bad rolls and praised for good ones, others will despise the addition of extra RNG to an already unpredictable game.

Lumar, One From Nowhere, The Unfathomable, Shines-In-Dark, Bliss-In-Ignorance

 A strange and obscure goddess from the mirror realm, which was once a blurred land of reflections in water and ice alone but has expanded with the creation of humans and their mirrors and glass and metal. Riikhites despise her for the creation of the moon, but is imitation not the sincerest form of flattery? No clerical powers reach into the mirror realm save hers, but regardless, she grants imitation miracles to visitors regardless, and they never know the difference.
not even once they've returned to the world of nonreflected light and shadow
Maybe there never really was a Lumar and the real holy spirit was inside you all along, kid
Or maybe the real miracles were the friends you made along the way?
knowledge drowned in the sea, better left alone
Something like that. 
+1 Favor- destroy knowledge of the true nature of the world and its purpose in the plan of the gods
-1 Favor- learn knowledge as to the true nature of the world
wrath- spread the word of the true nature of the world 
Common miracles- mental manipulation, illusion, moonlight and seafog and information, & planeshifting
BUT WHAT ABOUT CLERICS
The above rules are for everyone. Clerics are still clerics, but they're zealots, fanatics, who serve one god and one god alone. Their favor with their chosen god is indicated by their level and typical spells-per-day business, and while negotiating with other gods and spirits is part of their duty as religious icons, gaining favor with gods and spirits beyond their own is closer to 'leverage' than it is to a healthy religious relationship. 

BUT WHAT ABOUT ANIMISM 
Animism is great for this, though creating a pantheon of gods as factions is a lot easier than being prepared to run everything as a potential spiritual entity. Everything can potentially be a source of favor, be it an old ghost, a river, a tree, a stone, another PC, linguistic concepts... it's a rabbit hole that can go infinitely deep. Imagine Dungeon-as-God, where breaking down doors and strewing goblin entrails about infuriates the dungeon, but properly finding keys and arranging goblin entrails neatly may earn the favoritism of a dungeon. But this post is rambly enough as is, so let's call things quits for now.