In what cursory research suggests orginates from The Historie of Foure-Footed Beastes + accounts of grecian Khalkotauroi, the AD&D gorgon is a 'bull like creature' that breathes out a short cone of petrifying vapors, an attack they prefer to do over their 2d6 attack, presumably a gore/trample. Like many other petrifying creatures, they perceive into the astral and ethereal planes, and their petrifying effects extend to there.
There is not too much to say about them, save that a favorable stratagem, once their breath limit was realized, would be to force them into combat with something other than the party, then slay them once their petrifying abilities were exhausted.
AD&D Grey Ooze
This ooze is roughly in the middle of the deadly jelly-monsters of AD&D. Slow and easily dispatched by melee or ranged, its main defense is appearing as damp stone. It eats metal at the same rate as a black pudding, meaning dispatching it may leave the party unarmed and unarmored against later threats. It is immune to spells save lightning, and is also 'impervious to heat or cold' which notably removes burning oil as a solution and may waste a magic missile or the like. All in all, it strikes me as a creature intended to encourage versatility, backup weapons, and scavenging, but lacking the single-minded charm of the rust monster.
As a final note, some exceptionally large grey oozes attempt to psychically crush any psionics who dare to use this much maligned subsystem around them. While this seems to be more Gygaxian psionic-bullying, the idea of a monster whose size correlates with intelligence isn't bad, and were it applied to oozes that could split and combine this could be very interesting.
AD&D Green Slime
A properly horrific threat, green slimes are technically plants, and are indeed sessile apart from their 'drop from the ceiling' on people attack. Those who it attaches to turn into green slimes in 1d4 melee rounds, a transformation probably variable in whether or not the slime hits the bloodstream, disperses through the body, and devours the unlucky target from within in a flash. Plate armor adds 3 melee rounds before it is eaten through, and wood is very slowly eaten.
Removing attached green slime required scraping, excision, freezing, or burning. Cure disease kills it, but other forms of attack do it no harm (Though it may be reasonable to think plant-affecting spells would affect it as normal.) I thought sunlight killed it as well, but perhaps that was a later conceit made by GMs to assure green slime released into the wild would not consume the world.
It is barely a monster, more of an environmental threat, but it is a memorable one, and a reminder to players with Darkvision that having fire at hand is advantageous for reasons beyond light.
As usual, Goblin Punch has had some jolly good ideas on green slime, including their use as illegal bioweapon thrown in opaque flasks to nigh-instantly kill just about anything.
|Perhaps the horror of the green slime is a reflection of the horror of death and decay|
A corpse at least has a face, burial rites
someone eaten by slime is just gone in a flash, once a person with hopes and dreams
Now faceless slime, contamination
Sunset Realm Gorgon
I see no great reason to have this creature exist, as there is 'standard lore' for Petrification with regards to it being a sort of byproduct of Yg-based cognitohazards most of the time, and muddying the waters seems unnecessary.
The word, however, may exist in a more grecian/Sunset Realm terminology. Gorgon is the title/rank of a medusa who has forsaken scholarly pursuits, donned arms and armor, and gone to war for the Serpent Empire. So unless a campaign is to be set in the 2nd age when the Serpent Empire was still around, Gorgon is a term of historical note only.
As far as 'killer cow monster' goes I would still use my pandora's ox as a bull that wanders through a dungeon grazing on all manner of normally inedible, abstract things and gaining their powers for itself, and releasing a flood of corrupting energy if slain. The design goal of this creature being to
1- Be different every time, but thematically appropriate based on what it has eaten
2- Be a question of whether to let it roam and collect powers, risking it becoming too dangerous, or to kill it and unleash its corruption to make the rest of the dungeon more dangerous.
Sunset Realm Grey Ooze
As is, the grey ooze has no place, but I am inspired by the bigger=brainier idea, plus the depiction of slime intelligence from the manga Heterogeneous Linguistics, which is all about language and thought from 'monsters.'
While most slimes are unintelligent, ravenous maws of consumption, the Thinker Slime is different. It is unknown what causes an oozelike monster to gain intelligence, but it probably has to do with either eating books, or brains. Any slime can probably become a thinker slime, so this is not a specific 'type' of slime, but more like a template to apply to other slime monsters.
At human size, it has about human intelligence, stronger in pure memory and computational power, but lacking experience and context. It can learn social norms and speech much faster than a baby, but must learn them still. Each halving or doubling of HP roughly halves or doubles its intelligence, though it will often split into more slimes rather rather than seek the abstract heights of braininess unless it has a goal better served by a gigantic thinking jello.
It may split willingly, creating duplicates of itself, just smaller. Small duplicates of 1-4HP size are used as scouts which explore, then return and merge with the original to share information, or as an escape method in which the original sends out as many small versions to escape as it can, increasing the odds that at least 1 will survive and prosper.
If it is split unwillingly (typically by being struck by a bladed weapon) its intelligence and self is not evenly distributed among each part. If split in half, each half has a 50% chance of retaining any given knowledge the original had, with the other having that knowledge if this half doesn't. They may also reroll reactions, as they are essentially new beings, as might multiple slimes that re-merged back into a whole. Merging or splitting takes but a single round, but requires the round to be 'spent' by all involved parties.
They grow rapidly when fed, but require more feedings hence or will be forced to shrink under hunger's yoke. As a rough estimate, 100pounds of organic material(and/or whatever inorganic material this slime may dissolve) grants them 1d8HP after a dungeon turn of digestion.
Sunset Realm Green Slime
This menace is not a natural being, but rather, a nightmare vision of Life, mindlessly self-replicating, perfectly efficient, without any constraints on the simple eat-replicate cycle. It is, perhaps, a vision, a collective nightmare of Fauna imagining a plague-predator Flora. There are prophecies where the entire world drowns in slime, ancient ruins beneath the earth with no inhabitants save a single slimy colony of the stuff. Things have gone wrong with the Slime before, and will again. It is most common in Vint-Savoth, leading some to believe it is algae corrupted by the Blood Moon, or perhaps a variant form of Blood of that moon, but, deep enough in the bowels of the earth, it can be anywhere, dripping down through a thousand miles of hairline cracks and subterranean waters..
Taking this stuff into the sunlit world is a capital offense everywhere. Fools who seek to weaponize it invariably fall victim to it with the dramatic inevitability of a horror movie- it's not just dangerous, it's downright cursed. Political bodies that legalize its use in warfare are declared Dark Lords and crusaded against, much like what happens if some warlord has the bright idea to weaponize Moonspawn and other existential threats to humanity.
Still, fools rush in and all that, so with regards to adventurers, they should know that larger beasts take longer to be devoured- if a human takes 1d4 rounds, each doubling of mass adds +1 round to total conversion as the exponential flesh-to-slime conversion takes effect. Unlike a human being consumed, a monster or beast is likely to flail around as it is consumed, infecting all it collides with in its death throes.
The undead are unaffected by green slime, or at least, digested at a slow enough rate that a zombie leaking green slime is not a sight unheard of. Green slime that attains intelligence typically manifests as a Sludge Vampire (see goblinpunch posts above) and oft mimic real vampire behavior in an attempt to get people to waste their time with ineffective countermeasures. The Sanguine Church is aware of these creatures and suspects at least one vampiric lineage in Vint-Savoth is actually this type of blood drinking slime, as opposed to accursed human.