Juiblex is the closest thing there is to a deific ooze. It’s a creature of slime…and that’s its description in totality. Juiblex is pretty straightforward.
Its goals aren’t entirely clear because it doesn’t have a lot of interaction with sapient creatures. It’s generally believed that it wants to consume all things, not to destroy them but to make the universe one with itself, an infinite morass with it at the center. Progress is slow because its closest associations are with oozes, creatures who typically don’t have any religion or a plan beyond “I want to eat the thing.” Coming up with an interesting way to use Juiblex in a campaign isn’t easy, but that’s the task the designers intended, so here we go.
Typical/Atypical Followers: Juiblex’s followers are, almost as a rule, insane loners. Oozes aren’t the sort of creatures with whom one associates voluntarily. The best it can manage is the occasional cult who assumes they’ll somehow survive the apocalypse if they give it enough devotion and sacrifice. In truth, the best they can hope for is a slower, prolonged death. As such, literally everything is an atypical follower of Juiblex.
Plots: There are the obvious plots—oozes appear in a strange place, a person starts turning into an ooze, and so on—but “cult of slimes” will only carry you so far. Consider instead an actual, honest-to-goodness church of Juiblex, an organized group with ranks and goals. It’s hard, but it’s possible: maybe they want to call forth slimes to destroy specific enemies, or maybe they have a plan to survive the apocalypse in a specially-designed demiplane. If you give them some ability to direct or control oozes they become an even bigger threat. Imagine a thief or assassin who uses a black pudding to clean up evidence, or a monk who wards away weapon-carrying enemies with gray ooze companions. Present them as singularly insane antagonists, then leave just enough seeds for the players to trace back to a proper church they’ve never ever considered.
From the Vault: The ooze roster in D&D has always been somewhat anemic, but there have been some gems. The summoning ooze from the 3.5E Monster Manual 3 is a rare intelligent ooze, and it has the ability to create its own allies. To get a summoning ooze, take any ooze, give it an Intelligence of 10, remove one of its combat traits like corrosive form or corrode metal, and replace it with the demon summoning variant from a demon of an appropriate challenge rating. You can also give an ooze a quasit’s resistance ability to mimic an arcane ooze from the same book, or reskin a gas spore as an ooze to get the rupture ooze from the 4E Monster Manual 2.
No conversation about oozes would be complete without mentioning the oozemaster, a prestige class from the 3E splatbook Masters of the Wild. Probably intended for campaign villains rather than players, it lets a character slowly gain ooze powers in exchange for their sense of self. Over the course of ten levels an oozemaster permanently and irrevocably loses five points of Charisma, but it gains ooze features including attack powers that directly damage a creature’s Constitution score. To make an oozemaster, take any creature. For every two points you lower its Charisma, give it one of the following: a black pudding’s amorphous trait, corrosive form trait, or pseudopod attack; a gray ooze’s corrode metal trait or pseudopod attack, or a oche jelly’s spider climb trait or pseudopod attack. For every one point you lowers its Charisma, give it blindsight 60 ft. (blind beyond this radius) or immunity to one of the following conditions: blinded, charmed, deafened, exhaustion, frightened, or prone. Powerful oozemasters can use their pseudopod as a ranged attack, and you can also let them deal damage as though the target came into contact with yellow mold, brown mold, or green slime.