Couatl, Crab, Crayfish, Crocodile

OG Couatl-
Big snek, flies, poisons, goes ethereal, possibly can be a magic-use/cleric with psionic powers to boot just to ensure actually running would would require pre-generation or lots and lots of lookup. Also polymorph. They are 'considered to be divine' by the locals, and rarely involve themselves in human affairs. Also, groups of 1d4.

I actually like the 3.5 version more because it gives a list of said psionics and spells- Typically when I open a monster manual, I want to be able to run a monster immediately, not have to come up with spells and so on before it is usable.

Basically they seem like a very half assed take on 'high powered holy thing from a culture unfamiliar to the writers that has little to no connection to the player's experience.' From the wikipedia mentions of the things in D&D, this take seems to be fairly accurate to what has actually been done with 'em.
I think the bland vagueness of the Couatl is because it's not an original D&D monster like the beholder, but it's not a proper mythological being either. As far as I can tell, there is the word Coatl which is a Nahuatl word meaning 'Serpent' or 'Twin,' but no actual mythological creature of the name.
There is of course, Quetzalcoatl, but that's an entire god. Shockingly, 'magic wing snake who uses a distinctly biblical cleric spell list' doesn't seem an accurate depiction,

speaking of half-assed takes, have a half-assed snake

Sunset Realm Coatl
First off I don't got time for the "u"

Secondly, they are to snakes as classical angels are to humans. Wings are symbolic of transcendence of the material realm to ground walkers, and so Coatl have wings where snakes do not.

Quick Whodunit of cleric spells, assuming a mighty god with at least a city-state to their name
Level 1-2- ghosts of other dead faithful, very low level servitors also known as Cherubs
Level 3-5- dead prophets and saints, notable divine servitors of various power levels known as Angels. Coatl here.
Level 6+ The deity themselves.

In any case, Coatl roam the dream realm and afterlives of serpents, and occasionally guard ancient snake temples... but the serpent empire, like their goddess, was for the most part practical and material, so ancient serpentine bioweapons and soulless necromantic relics are far more common to guard dead and obsolete aspects of the serpent empire, while Coatl concern themselves with the protection of living serpent assets, occasionally rising from the shadow of serpent saints to defend them personally.

Basically this but with a serpent priestess and a coatl instead of three layers of internet memes
(I didn't have a tablet when i drew this but that doesn't excuse the anatomy uggggg)

In any case, Coatl need a quick statline that I can use since the monster manual's lame mention of spells and psionics is insufficient.
AC: As Chain
Move: As Horse in flight, and as half human while slithering.
HD-9
Attack- 1d3 bite+divine poison and/or 2d4 constriction
Big enough for one person to ride, though they'll be clinging to the coatl desperately, no limbs free.

Can fly and constrict/swallow prey at the same time, an expression of invulnerability to snakes who feel vulnerable when swallowing something. Coatl do not need to eat and typically will only swallow the faithful of Yg in order to bring them to the spirit realm for reincarnation as a snake.

If able to fly, a coatl can enter or exit the spirit world with a full move action, taking anyone riding or constricted with them. The spirit world is like the real world but as it is perceived by beings, rather than as it truly is. This means that being dragged to the spirit realm by a coatl will likely result in being dumped in an idealized snake-empire afterlife oneironecropolis, assuming the coatl was encountered in some ancient snake-ruin.

The divine poison of Yg is the will of the Mother of Serpents, not some mere chemical substance, and the following effects may come about when a Coatl bites someone.
Offensive Effects
Save v Poison and Coatl's choice of:

• Death via catastrophic organ failure. Undead immediately lose all (non skull) protections. This is a last-resort option used only on those who have well and truly pissed off the normally phlegmatic Yg.
• Feigned Death(awaken in 24 hours). Breathing undetectable but present- surviving in a sealed coffin for the duration is possible, but not underwater.
• Paralysis- of the 'floppy extreme weakness' sort. Only the voluntary muscles affected.
• Sleep- Awakenable via a round of slapping, shaking, cold water applied to face, etc.
• Blindness, Deafness, and/or Muteness- the damage is permanent, but reversible via herbal potions or Yg's mercy.

Beneficial Effects (one per bite)

• Remove poison, disease, blindness/deafness, paralysis, minor curses (real curses can only be lifted by esoteric requirements like 'when pigs fly') and other 'status effects'
• Heal 3d8 HP via shedding wounds. Requires some skin-shedding to ditch the itchy old wounded skin.
• Raise as servant (As Animate Dead). Such servants are animated by a mindless copy of instinct and act as bad-tempered snakes
• Stick to Snake (essentially an acceleration of the cycle of life, advancing from a plant to a snake, skipping a few stages of decay, growth, grazing, and predation in between.)
• Yg's Wisdom- Allows the bitten to speak/read any language while 'poisoned.' Can also relay complex information to the bitten if desired by the Coatl- knowledge of a dungeon map, or how to sail a boat, or the contents of a book, communicated through the blood directly to the brain.
• Bless- +1 to all rolls so long as the damage from the bite remains. Basically an adrenaline shot.

Giant Crab, Crayfish
 I don't have anything particularly interesting to say here. They have high AC and big claws. Players are often keen to eat them. On the Fault, there's a minor clan of free ogres who use blue giant crab shells as shields, and they probably serve as one of many sources of shell for the Ningen of the sea.

OG Crocodile
 A small and uninteresting entry, though the number appearing of 3d8 is certainly terrifying.

Sunset Realm Crocodile
Crocodiles are, like, various other reptilian species, essentially just snakes that did not give up their limbs to learn the wisdom of Yg, and therefore remained more animalistic and less snake-illuminati. Crocodiles also wisely refrained from participating in the promising but ultimately doomed 'Reptile Revolt' against said snake-illuminati and thus evaded the fossilized fate of their reptilian relatives, and the subsequent humiliating anthropomorphism inflicted upon the converted survivors. While Yg finds it useful to have servants with thumbs, lizard-people are as mud compared to a regular snake, their limbs and bipedalism a symbol of genetic penance, but more on them later in this series.

In any case, Crocodile skin is 10-100 times as valuable as leather

Croc leather armor as worn by Buckely, a rival adventurer from Crownless Lands. She got shot in the ankle by a PC called Ayrani and started a campaign of slander against 'Ankleshot Ayrani' that was pretty amusing. This doesn't have much to do with crocodiles but petty, grudge-laden but non-violent rival adventurers are great encounters to roll with and improv from.

 (moreso if passed off as dragon skin) and a common "+1-2 Leather" component , but many cultures restrict crocodile hunting to the priest-caste of society so that crocodile populations remain healthy and able to compete with other carnivorous monsters for ecological niches on the encounter tables. This tolerance waxes and wanes with the danger of the crocodiles to people, of course. Crocodiles in human and snake culture are often used as symbols of being set in ones ways and/or neutrality & passive acceptance of the status quo. Comparing someone to a crocodile is typically not flattering, but it's not quite an insult either- revolutionary groups have much better animals to make pointed similes with.