Giant Centipedes are the classic 'low level vermin introducing save or die poison.' They have a mere 1/4th of a HD, meaning 1-2 hp, and don't even deal damage, just save vs poison at +4 or die. While modern osr games often have death and dismemberment at 0hp rather than a flat 'you died,' if you were playing with random 1st level HP and immediate death at 0, centipede death venom is statistically safer than anything that deals HP damage of a damage die greater than your own HD.
Sunset Realm Centipedes
In ancient days of the 4th sun, the great goddess M'shesh, Mother of Undeath, had been driven from the waking world. Her temples were fallen or forgotten, her living cultists were slain, and her dead cultists were sliding into madness. She strode through the gloom of the spirit realm on the edge of Nightmare, far from the light of the outer or inner heavens, a thousand thousand of her followers following her tattered skirt. For every step she took, another soul was sent to her, screaming with the memory of being burnt by the light of the Tyrant Sun Riikhus, and another soul was lost to her, fading into the gloom, taken by some unknown temptation of the grey netherworld, perhaps to return someday, and perhaps not.
Before her was a deep swamp named Despair, and though her titan bones could wade through the murk, she feared for her tiny faithful. It was then that she came across a small heaven, dreamt by a mother centipede with a hundred children held in a hundred arms.
"I envy you, Centipede, for you can hold all that you cherish." M'shesh spoke, a hurricane.
The centipede waggled her antennae knowingly. "So too can you, Black Wind."
M'shesh looked at her arm-bones, each as vast as the mast of a ship built by giants. "I have but two limbs for this purpose, Hundred-Legs, but a thousand thousand children, and a thousand thousand more beings I wish to protect e'en tho I am spurned by they."
"She-Who-Bars-The-Way, this small one cannot help but notice you have a hollow skull, and broad shoulders, and spacious ribs, and a many-tiered spine, and wide hips, all which bear only sighs and echoes at the moment." So spake the little insect.
And then M'shesh was wiser than before, and she gathered up all her followers to her bones, and forded the swamp called Despair without a single drop of mud reaching her children. So it was that the faithful of M'shesh found their afterlife, the Osseous Scaffold, where they hang from the bones of the goddess awaiting rebirth.
All predators that care for their children are object lessons of how the sacred impulse to protect life can coexist with the profane impulse to hunt and kill to survive. Centipede iconography is the favored symbol of this in modern M'shesh temples (ancient temples tend to show large mammalian predators). Heretic undead (such as vampires) that create spawn by forcing undeath upon others are sometimes branded with centipede tattoos, or bound in centipede-themed manacles.
OG Cerebral Parasites
Cerebral parasites are another stupid gotcha monster built to counteract psionics in such a way that it seems blatantly clear somebody involved with the AD&D MM really disliked psionics in their game. They're invisible, removable via Cure Disease, attack and are unnoticed when doing so, and each one will drain psionic points whenever psionic powers are used and reproduce every 6 points drained. So basically you get invisible lice, lose your psychic powers and aren't sure why unless you have someone 'carefully inspect your psionic aura.' At least diseases and rot grubs have a bit of an advantage in stopping money-grubbing players from searching through trash constantly. (If you're wondering why that's a problem, consider that continual trash-sorting is a waste of game time that could be used seeking out actual treasures in actually interesting areas. But if your players all agree that trash-shuffling is great, you probably need to give them a treasure map rather than give them rot grubs.)
There are none in the Sunset Realms.
|fixed it now tho|
I was never a fan, really. 3 different AC's given with no explanation given, a full half-dozen relatively weak attacks simulating every single pointy end of the beast, and a 50% chance of firebreath. Also a number appearing of 1d4, another departure from the idea of the creature as a lonesome abomination. Not to mention Treasure type F which promises great treasures but usually delivers a single underwhelming result.
They just seem like a weird monster only good for the appearance of variety, while basically just being a nerfed dragon. Nothing really stands out beyond 'Hey you know that Greek Myth you read? Well here's a physical representation of that, stripped of the meaning and context of the original! Now hit it with a sword!"
And for whatever reason, I have it in my mind that a proper chimera has the head of a lion and a goat in front, and a serpent for a tail. D&D insists on a dragon instead of a serpent, and all three heads up front, and so that's all I have to say about that.
Sunset Realm Chimera
Though the classic goat-lion-snake-wing combo is well known due to a widely popularized but slightly misunderstood Beast Battle championship duel, the term 'Chimera' has both common parlance meaning any old mishmash of beasts, and an 'Official' definition which requires wings, 3 heads, at least 4 source animals(none of which may be humanish) and an unnatural origin. Chimera are not sterile, but as any potential mate must appeal to all heads of the beast, it is dashedly hard to establish breeding stock.
In any case, most chimera are not noble combinations of impressive creatures, but mishmashes of domestic animals created by mad alchemy for Beast Battler tournaments. Though there is no limit on creature combination, there are several common combinations that have gained popularity.
Rabamirel- A combination of rat, bat, mole , and squirrel. Cute and cuddly if you like rodents. Technically not a chimera, as they have only 2 heads.
Ultrabug- Spider, Scorpion, Centipede, Wasp. Terror/appeal/availability self explanatory.
Cagolope- A combination of cat, goose, and jackalope, these small but fiesty chimera are known for the wing placement which is commonly thought to be 'backwards' but when viewed as a quick backwards retreat option rather than a means of migration, the odd wing placement becomes intriguing in arena settings.
Crapmera-A combination of hyena, buzzard, worm, and pig(biting with the hyena head, charging with the boar tusks, flying with the buzzard wings, and waving about slimily with the worm-head tail) these middling-large-size creatures are considered filthy and unclean by a wide range of people, but are very easy to feed.
...And so on and so forth. If you wish to create a chimera of your own, the easiest method is to feed something a Potion of Fusion, throw it into a sack/cauldron with the things you want it fused with, and shake/stir vigorously- the animals willing to live on as part of an abomination will have heads, and those who depart the waking world will leave behind only wings, tails, claws, etc. Chimera created this way are notoriously foul-tempered.
The other method is similar to homunculous creation, in which the blood, eggs, spit, seed, etc of a creature (or creatures, in this case) is added to a sort of nutritious potion so as to create a rapidly maturing clone-thing that will have the disparate souls within satisfied with their body.
Since chimera add their mass together rather than averaging it out, adding in massive sea creatures can result in great success.