help me brainstorm, get a hug.

[Dreadfull]

So I'm going to run a short 3 to 5 session adventure for the players in my group. temporarily taking over for our DM.
They are at level 9.
Setting:
I like it pulpy and dark so that's the vibe I'm going for.
All the players are in a certain small city for one reason or another. Some are starting with a new character so only half the group knows each other in-game. Now in this city there is a monument of war at the center.
A long time ago this was the site of a huge magical battle that was the climax of an ancient war that has long since been forgotten. Under the city, unknown to the players the BBE lies chained in a tomb. Now topside a schizophrenic sorcerer who thinks she is an ancient mage has recently landed her fleet in the harbor and while the players are in the city she gets into a barfight (player actions will decide if they are there at the time) that pisses her off and drives her to breaking a dam further up the river that prevents the delta the city is in from flooding during rain season. It is rain season and the city floods. She then proceeds to lay siege to the city to exact her vengeance. (yeah its a massive overreaction but i need to keep my players in the city, they have a tendency to just up and leave when goings get tough).
The floodwater gets into the tomb and awakens the BBE This causes earthquakes. In session 2 he gets out. The players will have the first session in a flooded city that is being laid siege to do whatever they want. I don't like writing out too much but rather let my players do what they want and hook in on that.
The city is flooded so far you can only be on the roof of second story building or use the 3rd and higher floors if the building has them. the rest is water. It's a harbor city near the low point of a river delta so people here are somewhat used to deal with small floods and other water problems, just nothing this big. About half the people in the city die. The water will get putrid the more days they spend. There is very limited food and drinkable liquid.

Now I'm looking for help to think of more random encounters in a flooded city.

Ideas so far:
- a big roof with multiple commoners huddled together waiting for help. most are severely injured and the low level cleric helping them is at the end of his rope
- a fight between a store owner and his neighbor about what part of the roof they are on is owned by each of them.
- a few sailors who found several barrels of ale and are throwing a rowdy party
- the second floor of the church is still intact (this is an huge church with high ceilings) Only 1/3rd of the staff is still living. They are working hard to collect the dead and preventing disease to spread. The players can choose to help.
- Religious fighting is broken out in the temple district as groups of religious people are fighting over which god caused this, all blaming any but their own.
- 4 small rowboats containing what is left of the thieves guild are holding a diving expedition in the trade district looting whatever they can. this encounter might move to other locations if still alive later in the adventure.
- a giant crocodile took housing in the slums now its nest is washed away. Poor people are trying to escape for their lives all around the party while the croc seems to almost hunt them for sport.
- Sharks from the bay drawn in by the dead attack the players when crossing from building to building by water.
- a trade ship comes in only to run into the blockade made by the siege. A huge explosion seems to make an opening in the enemy lines.
- the players feel an earthquake (this is caused by the BBE trying to break loose)
- a riot breaks out as the city guard attacks the enemy siege and people loose most of the remaining defense force of the city. (if this one gets rolled the city will lose more and more of its order as time goes on)
- rotting corpses in the water has caused disease to break out. there is now an epidemic

The list goes on for a while more but i hope this gets the idea across of what I'm looking for.
I'm trying to fill a D% table so hope to reach 100 options but would at least like as many as possible. Can you guys help me with some additional ideas?

[Matuka]

May we know what the disease does? Is it a zombie contagen, is it a plague, or just the common flu? Also, how fast does it work?

[loki_ragnarock]

The rotting corpses should take a few days to resolve - give the PCs a chance to do clean up to prevent it from happening. Make this a known quantity.

Rather than make it a random encounter, put a piece of cardstock in front of your DM screen. Every X time that the PCs aren't actively working on the issue, add a unicorn sticker to the cardstock. Once you've reached critical mass of unicorn stickers, the plague of rainbow farts - so named because the diarrhea is multi-hewed and comes out in an arc - is unleashed. Very fatal. Very contagious.

Or use a different sticker and disease, but keep the general concept. If you like grim, make it dysentery or something; basically the same but less colorful.

Tie all the random encounters you throw together into this mechanic: your random encounters should give them a choice of how they help. Do they help the key NPCs in danger that will help with the siege, or do they help with the humanitarian issue that prevents the build up of corpses. Which is to say, take out another piece of cardstock, use a different sticker (lets say a thumbs up sticker), and track every loss of a key siege related NPC until you reach the line marked "Assault."

So, take your first one; civilians on a roof with a cleric. Take the cleric, make him valuable for the forces defending the place. Take the civilians, put them on a different roof. The PCs can tell that the next wave of flood water will take out both buildings. Time to make a choice; help the forces preventing the siege from turning into an assault, or help the people who will otherwise become corpses adding to the pile.

As another example, the rowdy sailors with ale. That ale can keep people alive in a time of siege. The sailors, gripped by the spirit of nihilism that comes from giving up hope in the depths of a siege, are willing to kill to keep the party going. Do the PCs save the ale by killing the Sailors and thus add a unicorn sticker, or do they just let the ale go and add a thumbs up sticker.

Make them choose. If your going for grim, make them choose. Ideally, make them choose between things that they care about equally, but rainbow farts or spear stabs are something everyone can care about.

EDIT
The croc one - sure you can kill the crock, but that's a lot of dead corpse that would otherwise be eating corpses for you. Kill the crock, save the people, get a unicorn sticker.
Choices are hard.

Further EDIT
Or nix the stickers and get out two jenga towers and make them pull a brick with every decision.
That'll start off low tension, but it'll build as you get through some things.

[Contrast]

I'm trying to fill a D% table so hope to reach 100 options but would at least like as many as possible.

How many times do you expect to roll on this table in your 3-5 session game? It kinda seems like with 100 you're going to be spending time thinking up content that you know will never possibly have any impact on your players.

Quickly looking up Xanathars list of beast forms of druid may expect to encounter in a swamp gives:

Migrating stirges
Giant toads
Snakes (of various types)
Rats (Diseased Giant Rat struck my fancy)

The table of random encounters also has some ideas - water elementals created by the loose magic, shambling mound wandered into the city, bullywugs or grung trying to sneak into the city (grung in particular could be either accidentally or on purpose poisoning a remaining water supply).

Other options could be encountering two bickering/fighting (depending if you want a social or combat encounter) druids - one trying to stop these unnatural floods/earthquakes and return the status quo, the other trying to reclaim the city for nature.

[Dreadfull]

May we know what the disease does? Is it a zombie contagen, is it a plague, or just the common flu? Also, how fast does it work?

It's called blood fungus (cause on of the PC's mother died to that he thought up the name I guess).
I was thinking of making it do the following:
It kills in about 1d3+1 days and infected people get disadvantage on saving throws related to all physical activities. It's airborne and starts in the lungs. It makes the blood turn greenish. It thrives in moisture and feeds on rot. But the mentioned rainbow sharts disease sounds like a great alternative.

[Matuka]

It's called blood fungus (cause on of the PC's mother died to that he thought up the name I guess).
I was thinking of making it do the following:
It kills in about 1d3+1 days and infected people get disadvantage on saving throws related to all physical activities. It's airborne and starts in the lungs. It makes the blood turn greenish. It thrives in moisture and feeds on rot. But the mentioned rainbow sharts disease sounds like a great alternative.

If the campaign lasts a second day in game, then I have an idea. After one day of being infected (because no matter what, the infected will live for at least two days.) The infected turn into zombies that are covered in thick layers of fungus, which gives them slightly higher AC then normal zombies. They can belch plumes of plague gas and there attacks do little damage but have a chance of infecting others with the disease (if they fail a constitution saving throw). When they die, either by running out of time or by a player slaying them, they crumble as diseased gas flows out of them. If they ignore the plague, there will be a higher chance of encountering them, if they take care of it, less of a chance.

[Dreadfull]

How many times do you expect to roll on this table in your 3-5 session game? It kinda seems like with 100 you're going to be spending time thinking up content that you know will never possibly have any impact on your players.

Quickly looking up Xanathars list of beast forms of druid may expect to encounter in a swamp gives:

Migrating stirges
Giant toads
Snakes (of various types)
Rats (Diseased Giant Rat struck my fancy)

The table of random encounters also has some ideas - water elementals created by the loose magic, shambling mound wandered into the city, bullywugs or grung trying to sneak into the city (grung in particular could be either accidentally or on purpose poisoning a remaining water supply).

Other options could be encountering two bickering/fighting (depending if you want a social or combat encounter) druids - one trying to stop these unnatural floods/earthquakes and return the status quo, the other trying to reclaim the city for nature.

I expect to roll from it a lot. Basically every time they move in the city without care. 100 might be a bit much, I know, but I like it when I'm not entirely sure what will happen either. And yeah 3 to 5 sessions doesn't sound like a lot but we play for about 6 to 10 hours each session. So guesstimating at about 20 times per session 100 options doesn't seem that far out. Also I already had 43 when I started this topic. With what I came up with in the mean time and the ideas I'm going to steal from your suggestions I'm already at 74 now.

[Dreadfull]

The rotting corpses should take a few days to resolve - give the PCs a chance to do clean up to prevent it from happening. Make this a known quantity.

Rather than make it a random encounter, put a piece of cardstock in front of your DM screen. Every X time that the PCs aren't actively working on the issue, add a unicorn sticker to the cardstock. Once you've reached critical mass of unicorn stickers, the plague of rainbow farts - so named because the diarrhea is multi-hewed and comes out in an arc - is unleashed. Very fatal. Very contagious.

Or use a different sticker and disease, but keep the general concept. If you like grim, make it dysentery or something; basically the same but less colorful.

Tie all the random encounters you throw together into this mechanic: your random encounters should give them a choice of how they help. Do they help the key NPCs in danger that will help with the siege, or do they help with the humanitarian issue that prevents the build up of corpses. Which is to say, take out another piece of cardstock, use a different sticker (lets say a thumbs up sticker), and track every loss of a key siege related NPC until you reach the line marked "Assault."

So, take your first one; civilians on a roof with a cleric. Take the cleric, make him valuable for the forces defending the place. Take the civilians, put them on a different roof. The PCs can tell that the next wave of flood water will take out both buildings. Time to make a choice; help the forces preventing the siege from turning into an assault, or help the people who will otherwise become corpses adding to the pile.

As another example, the rowdy sailors with ale. That ale can keep people alive in a time of siege. The sailors, gripped by the spirit of nihilism that comes from giving up hope in the depths of a siege, are willing to kill to keep the party going. Do the PCs save the ale by killing the Sailors and thus add a unicorn sticker, or do they just let the ale go and add a thumbs up sticker.

Make them choose. If your going for grim, make them choose. Ideally, make them choose between things that they care about equally, but rainbow farts or spear stabs are something everyone can care about.

EDIT
The croc one - sure you can kill the crock, but that's a lot of dead corpse that would otherwise be eating corpses for you. Kill the crock, save the people, get a unicorn sticker.
Choices are hard.

Further EDIT
Or nix the stickers and get out two jenga towers and make them pull a brick with every decision.
That'll start off low tension, but it'll build as you get through some things.

Making th disease known isn'tnneeded as it's something the players can easily find out but yeah eventually I will make it known if they fail to figure it out one way or another.

I love your disease idea but I already have a disease a player is familiar with. Seriously thinking about using both by now. Will definitely use the countdown concept to instill a sense of haste in the players. That's a great idea.

And yeah all encounters are pretty much open-ended because I was already thinking somewhat in that direction, as I like player actions to have consequences, but putting it in all of them integrates it even more. Huge thanks for the examples. I went through all of the encounters with this in mind and edited quite a few a little bit.

I don't have two jenga sets but im going to ask the party to bring one if they have it cause that idea is better than the stickers.

Thanks and hugs to everyone so far. This is shaping up to be a nice adventure.

[Matuka]

What are the BBEG's standard minions? Are there any wizards with water based experiments? What's a funny on water thing you saw in a movie once? Are there any nests of giant fire ants on the water in rafts made from dozens of other ants? That's 4 separate ideas for encounters.

[Tawmis]

- A female elf was pinned against a wall, from the rushing water, and drowned a slow and painful death; rises up as a Banshee (Over all not a threat to players at Level 9, but stopping her from wailing could save the common people, whom she may be attacking)

- The magic from the BBE has awakened a Water Elemental, who attacks anyone and anything (wild magic, so it has no master, no real purpose)

- The statue in the middle awakens, thanks to the magic from BBE (and turns out to have Stone Golem stats)

- A Grick Alpha (or several) have been washed out from beneath the city and are now swimming in the waters

- A Sea Hag (again, not powerful by default) has been drawn to the flood (looking to kill innocent people, attracted by the magic and transitivity of the entire situation)

- A hydra from a nearby swamp has caught the scent of dead and dying people washing into the swamp and is now investigating the situation

- One of the boats turns out to be a mimic

- A rust monster has taken shelter on a roof (same one as the guards, or the players)

- A Shambling mound washed up from a nearby swamp is furious to have its home destroyed, and attacking everything it sees

- The death toll attracts a Death Slaad

- Your crazed wizard is raising the dead so that the guards are forced to fend them off (so you have ghouls, ghasts, zombies, skeletons)

[Matuka]

All the bodies attract stirge swarms, Frankenstein-esc mad scientists trying to make a flesh Golem (if they ignore him he succeeds), evil spirits and other creatures that feed on the souls of the dead, blood thirsty sahuagin, furious merrow, giant vultures, and swarms of quippers.

[Matuka]

Also, what is the state of the prisons and asylums of the city?

[Matuka]

I hope we helped.

[SpikeFightwicky]

- Swarm of Stirges (use Swarm of Poisonous Snakes as a base, fly 40ft. instead of swim 30ft, instead of poison, up damage to 21 (6d6) -> 10 (3d6) at half HP to compensate for lost Poison damage, add the Stirge's "Blood Drain" ability -> if they hit, they stay attached for auto-damage next turn and leave when they've drained 50 HP. Fun twist: due to being a swarm, the player can't remove them (too many attached) and must jump in the water (or a fire) to remove them).

- A cleric is promising salvation from the disease if you convert to his religion, but the ceremonial "baptism" (held in private) involves the cleric drowning the would-be convert and raising them as ghouls.

- The strong magic and floods cause a gate to the elemental plane of water to open, causing water elementals to spill through and cause confused chaos.

[da newt]

Real world flooding is massive damage - few structures would be left standing, rushing water is crazy powerful.

Your first problem will be the epic 'survive the flood as it happens' - rushing water and debris, fires, saving as many people as possible ...

But why is the water still there? Why didn't it flow to sea? The town would need to be below sea level and only existed due to a massive dyke or something (insert magic if physics fails).

Post flood, the waters recede every day uncovering more stuff. I like the disease / undead stuff but maybe add in the race to find a cure (mystery) and then get everyone cured, all the while crazy lady is attacking ... Make it very hard for the party to rest, add exhaustion, make it realistic - combat may not be the primary threat to survival.

If the flood source is river - then fresh water, but if the flood is due to a broken dyke (or magical tsunami / Tropical storm) then you can input all sort of ocean creatures.

Think Katrina or any of the recent nasty tropical storms.