An actual D&D thing I made
Exposition
The Mayo Cult control the records and history in the world´s libraries. They made up the legend of the Mayo Hero so that they could get the entire world to preach their god. They want to flood the entire world with mayonnaise and drown everything, so that their god can have a plane to inhabit. An ancient being, made out of coal (The opposite of mayonnaise) remembers the truth and sends the party to deal with this cult.
The cult´s base of operations is no secret, it is in the middle of the capital city of the neutrals. A gigantic mayonnaise fountain feeds the people, supplied by an unknown source. People are sacrificed in the hopes that their blood will be converted to mayonnaise through alchemy, and the cult have cut off every other food supply. The old ruling party is dead, but nobody who knows that information is left alive and the people are too entranced with the mayonnaise to care about their disappearance.
Entering the Town
The party will be stopped entering the city by 8 cultists, who will try to take them into questioning. If attacked, one blows a horn which summons 4 more in 1d4 rounds. Statblock:https://imgur.com/a/J1hb1Uq
If the party goes along with the mayonnaise cultists, they take the party to the mayonnaise room. This room is utterly empty, and every surface is coated in mayonnaise. There, they question the party. A series of contested persuasion or deception checks are required for the cultists to allow them to pass, otherwise the cultists will schedule them to be sacrificed in 2 days via burning the mayonnaise room. At this point, the cultists will lock the party in the mayonnaise room where they can simply leave by kicking down the door (Mayonnaise has weakened it over time).
I´m sure you have the town planned already, and you can improv the effect the cultists have had on the town, so here´s the main attraction if the players go
here:
The Dungeon
The mayonnaise fountain. It is a massive edifice in the middle of town, with a large ziggurat leading up to it. Two gigantic doors lead into the ziggurat. One leads to room 5, one leads to room 1. If the players choose to swim down the drain in the fountain, they will end up in room 8. Roleplay the townspeople marvelling over the Great Fountain, and they might just go in. Both doors are locked, requiring a DC 18 Strength Check, flame, or thieves´'tools.
Room 1: Opening the door, the party is met with a wave of mayonnaise. Anyone standing in front of the door must make a DC 8 strength check or be knocked prone and take 1 bludgeoning damage. The room is difficult terrain until all mayonnaise drains in 8 rounds. A locked door is 20 feet ahead, and the room is 15x20 feet. Once the door is opened, initiative must be rolled as 1 cultist ignites the mayonnaise with their Rifle of Flaming Mayonnaise and the rest fire at the party. The fire spreads 10 feet per round in every direction. Characters starting or ending their turns in the fire take 1d4+1 fire damage. At the same time, 1d6 cultists outside notice the commotion and reach the party in 2d4 rounds.
Room 2
:This room is a circular room 30 feet in diameter, with a small fountain of mayonnaise in the center. stone statues of eldritch deities coated in mayonnaise adorn the corners, and jars of mayonnaise dwell on shelves dug into the walls. Strange glyphs cover the inside of the doorframes. 4 cultists are here, who were drinking mayonnaise but are now warned of the party. 3 stay and fight, and 1 warns the rest. Each doorframe has a Glyph of Warding on it, the front and back doors casting Grease and the side doors casting Scorching Ray (+4 to hit / 12 spell save DC). Cultists are specifically exempt. The cultists will try to bait the party through these doors, and then set the grease alight and stab prone party members. If they are losing the fight, they will split in three directions and lock every door except for the one that the party entered from to buy time. The back doorway leads to Room 3, the right leads to Room 4, and the left leads to Room 6.
Room 3:
This room is a long corridor, 10 x 50 knee-deep in mayonnaise making it difficult terrain. Arrow slits line the sides of the walls. A murderhole is on the left side of the doorway. There is actually a crawlspace ABOVE this room, and a cultist will drop down on the other side and lock the door once the players enter. Then, burning mayo will fall from the ceiling (Triggered by the cultist closing the door). The fire will spread at 10 feet / round, and the cultists will shoot through the arrow slits at the party. 30 feet into the corridor is a pit supported by fragile flammable supports, dropping 60 feet into the city´s sewers. These supports will be burned through in 3 rounds. At the end of the corridor is a single cultist. Behind them is a door leading to the crawlspace that the arrow slit cultists are in. They will come to support the remaining cultist 1 round after the party finishes the corridor. Creatures caught in the mayonnaise fire take 1d6 fire damage every time they start their turn in the fire. The hallway leads to room 7.
Room 4:
This room contains 2 gibbering mouthers, covered in mayonnaise. A cultist is currently pouring mayonnaise on the gibbering mouthers, and will run once the party arrives and release them. The reason that the cultists are keeping gibbering mouthers covered with mayo is that they remind them of their god. A mixture of gibbering mother and mayonnaise coats the floor, making the room difficult terrain. When fighting the gibbering mouthers, every remaining cultist in rooms 6 and 7 will arrive to assist them in 1d6 rounds. The doorway here leads to room 2 and another leads to Room 8.
Room 5:
This room is identical to room 1, leading to Room 4 instead of Room 2
.Room 6:
This room is a 30 foot diameter circular room. A pedestal is in the middle of the room, with a statue of what appears to be a gibbering mouther covered in mayonnaise. Cultists who were praying here have readied actions to fire with their mayonnaise rifles. Alchemy jugs on the pedestal are currently pouring out mayonnaise, though it is not in large enough quantities to make the room difficult terrain. The cultists here run in all directions after taking shots, locking doors behind them (DC 16 to break down or thieves´ tools). Once the cultists have left the room, one uses a tunnel to activate the flaming mayonnaise cannon. This cannon takes 4 rounds to fire, but once it does creatures on the pedestal take 3d6 fire damage and 2d4 at the end of their turn until they put it out, and creatures of of the pedestal take half. There is no save. After firing the cannon, the room is difficult terrain until someone cleans it up. There is an extra cultist on every door for every round the players stay in the room, for a maximum of 2. The doorways here each also serve as guillotine traps, triggered by releasing a rope on the other side. Creatures under doors when the rope is released take 2d6 bludgeoning damage and are pushed back 5 feet. The doorways here lead to rooms 7, 9, 10, and 11.
Room 7:
This room is a square room 60 x 60 in diameter. Sleeping rolls are laid on the ground every 5 feet. 4 cultists stand on the opposite side of the room, ready to flee.
Room 8:
This room is a cliff with a staircase leading down. At the bottom of this stairwell is the resident Necromancer (Level 3 Wizard you choose what they have prepared), with their 4 pet zombies and ghoul. A hole in the ground leads to the sewers at the back of the room.
Room 9:
This room is a 5 foot rim around a massive pit. It is said that this pit is where the mayonnaise god will rise up from, and so the cultists here will fight to the death in the hopes that they will get a mayonnaise-filled afterlife. There are 6 normal cultists, and two sorcerers with the following prepared: Gust of Wind, Message, Create Bonfire, Light, Prestidigitation, Fire Bolt. They set fire to the thin layer of mayonnaise here to block off members of the party and then use Gust of Wind to attempt to push people into the pit. The pit is 600 feet deep, ending in an underwater sea of mayonnaise. This mayonnaise eats whatever falls into it, dealing 1d6 acid damage to whoever somehow survives the fall. A DC 16 athletics check allows someone to climb up out of the mayo, at which point they can make a DC 14 athletics check to find a ledge that they can stay on. At this point, they will require assistance OR a series of 15 DC 12 athletics checks. The doorway here leads to Room 10.
Room 10:
This room is 100 x 90. A kitchen resides on one side, and sleeping rolls on the other. 6 cultists attack here. A doorway leads to Room 11, and a secret door leads to Room 11.5 which requires an Investigation check to find.
Room 11:
This is a short hallway leading to Room 12. It has 4 pit traps, each dropping 30 feet.
Room 11.5:
This is the actual hallway leading to Room 12. It is unguarded.
Room 12:
This is the shrine of mayonnaise. The fountainmaster (Who is a human entirely made out of mayonnaise and scaled up) and their servants reside here. They are currently drawing symbols out of mayonnaise on the ground, seemingly trying to summon their god. If the players don´t attack within 4 rounds, they summon the mayonnaise god and the entire world is destroyed. There is the fountainmaster, their 2 sorcerer companions who have the same spelllist, 10 cultists, and a rudderkin MADE OUT OF MAYONNAISE. The rudderkin has resistance to nonmagical slashing and immunity to nonmagical piercing, but has 40 less hp and lacks their fear effect. Statblock for the fountainmaster:https://imgur.com/a/IfDBrsXDoorway leads to Room 13.
Room 13
: This room is a 60x60 storeroom of alchemy jugs spitting out mayonnaise all of the time. This is what fed the city, before it probably got destroyed in the fight. The players are free to take as many alchemy jugs or mayonnaise as they wish.