There’s a lot more information on the realm that Juiblex rules rather than Juiblex himself. It seems like nobody is sure what to do with him.
AD&D Monster Manual
- He can fly! That must look strange. Maybe he turns into a sphere?
- Once every 10 rounds, he can spew forth a slime that is a combination of an ochre jelly and a green slime.
- He can spread himself into a pool of slime or become an 18-foot-tall "column of disgusting ordure."
It says here that on Juiblex's plane there are slimes, deadly puddings, jellies, and various amoeboid monsters.
Throne of Bloodstone
This adventure is nuts. Tons of info on the Abyss!
The Realm of Juiblex: "The nauseating stench of decaying matter greets you…" This place is filled with fungus and rot. It is sometimes known as the Amoebic Sea.
- Every 30 minutes, characters need to make a save or suffer the effects of a stinking cloud spell.
- The layer putrifies all non-magical food. Water is turned into gelatinous cube material (!). Food becomes black pudding. When that happens, they eat through your stuff and attack you!
- Stepping into the swam causes you to duffer the effects of: Green slime, yellow mold, ochre jelly and black pudding.
- If you fly over the swamp, it spews great columns of muck at you.
- Giant Obliviax: It drains your memories from the last 24 hours and memorized spells.
- Giant Gelatinous Cube: It's 100 feet to a side!
- Green Slime Colony: Lots and lots of green slimes.
It actually lists the treasure in Juiblex’s Palace. It includes an alchemy jug, pipes of the sewers and a talisman of ultimate evil.
They changed Juiblex’s stats. In the Monster Manual, he had 88 hit points. Now he has 176.
Juiblex is described here as a lesser god. He spreads disease and is beyond mortal comprehension.
Some aboleths revere him, because Juiblex is slowly revealing lost magical secrets to them and the aboleths believe that he keeps their skin moist.
There’s a mention of quintuplet tieflings who tried to use a building (known as "The Rotting Oracle") to channel information from Juiblex. The building sunk halfway in the mud and the tieflings disappeared.
Faces of Evil: The Fiends
The alkiliths are thought to be the creation of Juiblex.
The Inner Planes
There is a portal to the Para-Elemental Plane of Ooze in Shedaklah. The portal is a gelatinous orb 30 feet across. If you press a platinum disc to it, the portal activates. Weirdly, the person who activates it can't go through.
Juiblex has made an alliance with Bwimb II, the princess of Para-Elemental Ooze.
Planes of Chaos
Shedaklah, the 222nd layer of the Abyss. The Slime Pits:
- Vast expanses of caustic and unintelligent slime.
- Strange organic forms rise from the ocean of molds at Juiblex's whim.
- Juiblex shares the realm with Zuggtmoy, demon queen of fungi.
- According to this, Zuggtmoy is still trapped in the Temple of Elemental Evil.
The caverns under Shedaklah are a perpetual battleground of oozes and fungi.
Dragon Magazine #358
You can sail the River Styx between the Slime Pits and the area of Shedaklah that Zuggtmoy rules. On the shore by the Slime Pits, the river jellifies with acidic and predatory slime.
Juiblex's Grasp: There is one area of the Slime Pits that is a shallow bay of slime that covers a forest of mushrooms. The flow of slime can create riptides and undertows
Book of Vile Darkness 3e
We learn all sorts of stuff about Juiblex:
- Other demons refer to him as the "Lord of Nothing."
- He does not scheme, he is content to simply exist. He hates everything and revels in destruction.
- There are a lot of hezrous that serve him. They bring victims to Juiblex to feed on.
- Juiblex often takes the form of a 9-foot-tall cone of jelly and slime.
- He is nothing more than a seething pool of animate ooze.
- He has pulsing red eyes that look in all directions.
- If possible, he starts a combat invisible and engulfs a number of foes at once.
- His touch does 50 acid damage to wood and metal per round.
- He can exude a circle of cold, all within 10 feet take 6d6 cold damage per round.
- Once per round he can spew forth a patch of green slime.
- If engulfed, you can actually drown inside of Juiblex.
- She can spit caustic goo, exudes acidic slime from her hand, and she secretes a smelly ooze from her pores.
- Once per day she can summon a demon.
- She can also summon a patch of green slime, a gray ooze, an ochre jelly or a gelatinous cube.
Fiendish Codex I
- Juiblex is the lord of oozes and shapeless things.
- Most weapons can barely harm him. He is immune to bludgeoning damage.
- He can spew green slime at foes and summon both oozes and demons to aid him in battle.
- He is at war with Zuggtmoy.
- It has an overcast sky of mud-brown dotted with rotten green clouds. It rains polluted water and everything in the realm is covered in a thin slimy film.
- It says that while Zuggtmoy was trapped in the Temple of Elemental Evil, Juiblex spread throughout her layer. Now she is back and she is trying to drive him and his minions underground.
- Shedaklah is actually infused with life-giving positive energy. All living creatures gain enhanced healing abilities... "fast healing 2" in 3e terms. Maybe in 5e you can spend healing surges as an action, no rest required?
The Ichordeep Entity: A lowly expanding strain of colonial algae that can use giant pseudopods to pull flying creatures down from the sky. Zuggtmoy may have no control over this thing.
The Slime Pits of Juiblex: Five bubbling slime-filled chasms that "erupt onto the surface of Shedaklah like pus from a broken scab."
Xhubhullosk: A mortal settlement! An assortment of lean-tos and rotting stalk structures. It is home to 400 people who became stranded on this layer somehow. Myconid servants of Zuggtmoy guard them and try to convert them into worshipers of Zuggtmoy.
Zuggtmoy's Palace: Her stinking palace is made from the largest fungi in the multiverse. It's four miles high!
Aspect of Juiblex: When he has to make an alliance with another demon prince, he sends an aspect along with a succubus for negotiations. They're guarded by two vrocks and two black puddings.
There are two new spells:
- Oozepuppet: You can telekinetically take control of an ooze.
- Slime Wave: You create a wave of green slime that more or less summons about 6 green slimes. Once the wave hits you, the slimes need to be removed from your body in one round, or else you'll need to burn or freeze them off.
We actually get some major storyline developments.
Zuggtmoy created adamantine plinths and triggered a ritual meant to banish Juiblex to a different plane but it didn't work right. A portion of Juiblex's polluted form was sent to the Elemental Plane of Water.
This polluted a section of the Plane of Water and created the spawn of Juiblex there. Those creatures eventually were banished themselves by denizens of the plane to a demiplane of filth. This demiplane is a forest with ground of pulsating slime and streams and ponds of reeking watery goo. There's a green sun and great clouds of insects in the air.
The Hermit: At the center of the demiplane of filth is a monolith that has a hut on it. That is the home of The Hermit. The Hermit was made from a single shard of Juiblex's essence and he knows a lot about the multiverse. He's an avatar of Juiblex.
When he talks, green slime leaks out of his mouth and devours his body, but he is reborn somehow.
Dungeon Magazine #132 - Caverns of the Ooze Lord
This issue has an an adventure called Caverns of the Ooze Lord We get some details on what a shrine to Juiblex is like.
There is an old cleric named Morbion who lives in the woods and is obsessed with slimes and oozes. He explored the "Sickstone Caves" where he found an olive slime, which turns those who touch it into olive slime. He's been infecting villagers with olive slime, which slowly turns them into slimes.
Olive Slime: An immobile ooze that attacks with tendrils that cause paralysis. It grows in the flesh of those it touches.
- It is immune to non-magic weapons, lightning, poison, and most forms of magic.
- Olive slime and green slime neutralize each other when they come into contact.
- Secret Shrine: There's a secret shrine to Juiblex under a temple in a town. It has a long stone block fitted with chains and manacles. The cultists burn incense that gives others penalties to rolls. They have a silver urn with an olive slime in it.
Second Shrine to Juiblex: The walls glow with silver green radiance. The floor is a mire of ooze and slime. The walls weep a dark green liquid that runs down in rivulets.
The altar is made of glowing green stone. Four black candles burn with lurid green flames.
Dungeon 181: Demonomicon of Iggwilv - Juiblex
Titles: He Who Slithers, the Unnameable One, Glistener, Indescribable Darkness, and the Slick of Foulest Humors.
Dagon and Pazuzu think that Juiblex was an obyrith that Tharizdun shattered, but this is not true. Juiblex was an infection in a wound of the Elemental Chaos, a mass of gel stirred into awareness when Tharizdun lodged the seed of evil into the Abyss.
Juiblex witnessed the formation of the Abyss and the battle between Tharizdun and the obyriths. Juiblex knows the true name of each obyrith! Wow, that would include Pazuzu and Obox-Ob.
Juiblex has slimes everywhere, in every realm. He ha so many of them that he cannot command them all. He is slowly accruing power and once he has enough, "the cosmos is doomed to drown in his putrescence."
Juiblex has the ability to possess oozes and transform them into an aspect of Juiblex.
Shedaklah Notes: The pits contain lakes of slime. The oldest of these lakes is called Suppurus. It is 100 miles across.
Juiblex has a sort of throne room. There is a cracked stone pedestal that he perches on. It’s pretty shabby.
Denizens of Shedaklah include hezrous and pod demons.
All of his humanoid servants are touched with disease in some way.
Ooze Scion: A minion. When it is hit, roll a d20. on an 11 or higher, it takes no damage and a new ooze scion appears next to it.
We get stats for Darkness Given Hunger. It is the mightiest ooze next to Juiblex. When it is dropped to 0 hit points, the ooze is destroyed and the hezrou inside of it stands up and attacks!
Spawn of Juiblex: When these slimes die, they are reabsorbed by Juiblex and are born again. They are living extensions of Juiblex. Aboleths and otyughs are drawn to them.
- Ooze Horror: It has a thousand eyes and it can fire acid globules and cause fear-based psychic damage.
- Plague Hurler: It call forth a rain of effluvia that will blind you. This thing can actually take the form of a humanoid that it has seen. It can shoot virulent pustules as a ranged attack, infecting you with:
- Slime Lord's Rot: As it gets worse, your movement is lessened. Eventually, you die and become a sludge dredge.
- Sludge Dredge: This is a one hit point minion. When it dies, a dead sludge dredge within 30 feet is restored to life. That's pretty crazy.
Wow. There's a whole thing in here. Juiblex has apparently acquired another layer of the Abyss.
Molor, the Stinking Realm: Juiblex is the opposite of Erathis, god of civilization. Juiblex is on the losing end of the struggle with Zuggtmoy.
Thullgrime: A town in the twisted tunnels. It is home to cultist explorers, wererats and "disease-riddled consumptives." In some places, the ground is alive and drags creatures below. Eventually, their bones bubble up to the surface.
The place is ruled by Cullis Heartrend, who is served by a creature known a the Grollog, a huge amorphous beast with dripping pits for eyes. It is somewhat intelligent and can communicate in broken Abyssal and Common. Nobody knows why it serves Cullis.
Dripping Tunnels: Filth of all sorts flows here - stinking waste, diseased refuse, rotting food...
Juiblex's Shrine: Worshipers come here to pay homage. The shrine is said to hold uncounted riches beneath it. Followers have been tossing offerings into the slime for centuries.
The Maw of Eternity: A cavern with a 15-foot-wide hole in its center that is said to be a bottomless pit. When you jump in, you fall for ten minutes and pass through an unpredictable portal that sends you to a random layer of the Abyss. Sometimes it sends creatures beyond the planes entirely.
Molor is linked to Shedaklah through a number of portals.
Out of the Abyss
The Oozing Temple: This place is a forgotten temple that is home to servants of Juiblex. There is an intelligent gelatinous cube here name Glabbagool and it can speak via telepathy. Juiblex's arrival in the Underdark has granted it sentience. It might join the group as an NPC sidekick.
The Pudding King: A deep gnome who lived among oozes. He named some of them. Princess Ebonmire is a black pudding and Prince Livid is a gray ooze.
When Juiblex arrived in the Underdark, he threw himself down and pledged loyalty. Juiblex gave him the power to command and summon oozes. He summons oozes to The Pudding Court and prepares to overtake the settlement of Blingdenstone.
The Fetid Wedding: In this chapter, Zuggtmoy is going to merge with this thing called Araumycos and become very powerful. Juiblex and the heroes can stop her.
Spies: Juiblex has two black pudding spies, which is weird.
Juiblex Stat Notes:
- Those consumed by Juiblex are obliterated.
- Seeing him might cause you to go mad. Effects include the need to consume everything, and refusing to part with any possessions.
- Juiblex can eject a corrosive slime that does 55 damage! It can pull you into its body. You are obliterated within one minute.
A very handy rundown of Juiblex's history in D&D.