1. Don't Mess with Druids
An Aquatic Elf Druid has become enraged with the people of McCoastalTown who have been unknowingly and unwittingly fishing, crabbing, and/or dredging for precious metals/ores in her underwater grove, and she's taking this personally and now plotting her revenge.
GM's Notes: Depending on the level that this encounter is used, it can range from Lesser Water Elementals attacking at night, to Nymphs serving the Druid by charming the Mayor and city officials, to the Druid sending a 1,000-ft Tsunami
2. Haunted by the Past
A passenger/cargo ship crashes into the docks/pier/shore at over 20 knots. Upon investigation, the PC's find that the cargo is gone, the captain, crew, & passengers are all missing, the shipping manifest has been stolen/destroyed, and all of the ship's port-of-call receipts are missing. The captain's parrot is apparently the only survivor of this debacle and remains with the crashed ship, and he stays perched on the ship's now-partially-destroyed crow's nest, and continually squawks nothing but "batten the hatches, set yer deadlights", "kiss the gunner's daughter", and "dredgie's come te get ye" over and over. If approached, the parrot attacks in a feral, territorial manner and screeches "Offa my ship! No quarter for landlubbers!".
GM's Notes: "Batten the Hatches, set yer deadlights" refers to an unnatural storm, "kiss the gunner's daughter" refers to a harsh punishment where a crewmate is disciplined by being tied to a cannon and flogged, "dredgie's come te get ye" refers to the Ghost of an unfairly killed soul coming to haunt the ship. A crewmate died during one such flogging for a miniscule offense, and has vowed to drown the captain and his ship for good. The ghost caused a storm that wiped them all off of the ship, and now the crew/passengers are marooned them on a chain of island a week prior, and they're going to start starving soon. Upon the PC's investigation at sea, they find that the flotsam from the ship's cargo spans for hundreds of miles, and there are pirates already attempting to loot the goods.
3. Unorganized Labor or Slave Wages?
The Longshoreman's guild has recently elected a new president and then subsequently doubled their rates. If the Port's customers refuse to pay, then the newly-formed militant gang of the Longshoreman's guild either has a "Boston Tea Party" with the ship's cargo or they barge into the non-paying-crew's room at the Tavern's Inn in the middle of the night and introduce them to a 7-course meal of knuckle sandwiches.
GM's Notes: The Longshoreman Guild's new president has been running a boxing/wrestling club at night for nigh a decade to make ends meet, and has recently been training its members to become brawlers and grapplers. They're sick and tired of all the long hours for nothing but coppers, and this president has promised more pay and better livelihoods by any means necessary. On the surface, the Tavernkeeper is outspoken against the night raids in his establishment and locks the doors at night to "prevent the unnecessary violence" from the Longshorman's guild, but he's actually the president's friend, and sneaks them in/out undetected.
4. Don't Mess With Druids II
A local town or city has polluted their cove and harbor with run-off sewage, trash, and other debris to where a local druid (aquatic or not) has come to the aid of the sea-life and nearby aquatic people.
Using powerful magics, he's constructed a magic item that filters out most waste and pollutants as well as some trash. This item could be anything reasonably water-resistant, such as an anchor buried in the mud somewhere in the harbor or even a gemstone or stone disk.
Every night, sometime in the darkest part of the night after midnight, the magic takes all the filtered scum, sewage, and small trash and magically 'mists' or transports it evenly over the town. It's not a tidal wave, but like a fog that phases in. When it leaves, all the walls, roofs, and streets and coated in filth. This disgusting coating is like a gluey paste and doesn't wipe or wash off easily.
Even when the townsfolk do clean some of it off, it eventually washes back into the bay or harbor and over the day gets collected by the magic, only to be returned along with any other waste from that day, slowly compounding the filth the next morning.
Townsfolk have taken to wearing perfumed masks, but this still requires regular Fortitude saves or be affected as though sickened and, at particularly harsh times of day, such as when it's very hot, this can even become nauseating for a time.
GM notes: The magic items causing this might be located eventually, but it may also be guarded by an aquatic protector, like a shark or octopus, possibly even an animate aquatic kelp or plant. Either way, relatively harmless fish or other creatures will alert the druid that it's being disturbed. He'll send a message via an aquatic (and bubbly) version of whispering wind to leave it alone until the town learns to clean and purify their own filth and stop discarding so much trash into the water.
If the town eventually channels some funds or raises some taxes to pay for a magical/medieval-style water treatment plant (or basically a cistern/waste pool that some priests purify before releasing it into the by/harbor, the druid will remove the 'curse'.
5. The Ghost Ship
Sightings of a ghost ship have been reported in the area and the legend of a bloodthirsty pirate who vowed to slaughter the town have resurfaced. Many people have fled the coastal village (or the wharf/dock area of the city), leaving only desperate people who refuse to open their hovels or come out at night or nefarious skullduggers (all with a tale of the ghostly pirate captain and why or how he planned his revenge) lurking in a seedy tavern.
One moonless night, the eerie glow of ethereal light illuminates a tatter-sailed ship sailing outside the port. Blood-curdling cries and whispers of promised death echo over the waves of the port. If the dock is part of a larger city or protected by a lighthouse, tower, or possibly a patrol ship, a fireball of glowing green balefire streaks out and blasts into it once or twice, causing any defenders to flee or at least cower out of sight. Anyone able to move will flee in terror from the area.
GM's note: An enterprising band of robbers has come up with a scheme. Using a simple rowboat or dinghy, they've used a wand of illusion to cloak it as a ghostly ship using an apprentice mage of minor prowess. In the case of a defended port there are two, with the second wielding a modified wand of fireball which produces the greenish balls of flame. The main band spends the hours of terror in the night looting and robbing. If accosted, they pretend to be frightened sailors just trying to carry their personal possessions and fleeing with the rest of the townsfolk. If PCs investigate the ship and try to land upon it, they likely pass through and discover the ruse (likely after a dunking). The apprentices will have slipped into the water, either using waterbreathing potions they've imbibed earlier or just really high Athletics skill focuses on swimming to make their way underwater to the shore.
This same event occurs the next night if the plan goes well. If the ruse was discovered, the heightened hysterics have actually summoned a true dread pirate ship (which fires ghostly cannons with similar appearance to fireballs) and is crewed by actual undead spirits. They will eventually, if not stopped on the ship, come sweeping out over the harbor and whirl through the streets of the dock area terrorizing people (though they don't necessarily go for kills, they will swarm any 'heroes').
6. The Fate of Constance Kesselbeck (CR15+)
Some 10 years ago, Admiral Constance Kesselbeck was reported to have gone down with her ship while fighting a Kraken near McCoastalTown, however that story is all about to change. Townsfolk (and the PC's as well, if they spend the night in McCoastalTown) have been reporting highly vivid dreams and nightmares; in the dreams, they see the Admiral ethereally walking on the water near the Monteursor Archipelago, a long series of islands approximately 8 days-worth of sailing away from McCoastalTown. However, in the nightmares, they see two particularly evil Illithids, a pair of famous Mind Flayers named Phaequum and Tsazzeng'noth, who are torturing her mind and driving her to madness.
Townsfolk (and the PC's) have a 50% chance of having a nightmare whenever they sleep, and each time they have a nightmare, they become possessed by the Mind Flayers (Will DC: 20 negates, anything that can remove Dominate Person or Mind Control can also remove this Enthrall effect), and once possessed they make every attempt to fly, sail, or float to the island in the archipelago and become their Thralls. The Kraken will attack anyone while enroute who attempts to visit the archipelago who isn't enthralled by the Mind Flayers.
GM's Notes: Phaequum and Tsazzeng'noth have based themselves in an underground lair on one of the islands in the Monteursor Archipelago, and they are famous because every 5-8 years for the last 30ish years, they've held one of these "mass possession events" where they either decimate or completely annihilate populations of cities with this exact tactic. They turn townsfolk into their mindless slaves via nightmares who then attempt to reach their master's side, and any resistance from the city during this "mass possession event" is dealt with by the Kraken that is under their control.
Constance Kesselbeck did go down with her ship, but she survived as one of these Mind Flayer's thralls. The Mind Flayers are using the Admiral as the reagent for their Psionic Manifestation of the homebrew spell Mass Enthrall by assaulting her mind and projecting it to all the people of McCoastalTown. When the townsfolk/PC’s have a dream instead of a nightmare, it is Constance’s Will power fighting back against the Mind Flayers influences, and she’s attempting to send a message in the dream of where their island base is located.
When the PC's go to confront the Mind Flayers, their ship will be attacked by the Kraken enroute. It takes 8 days of sailing to get there (***Why 8 days? Because unless you have an airship, flying for 8 days nonstop is somewhat hard to come by. You want the PC's to be "as forced as possible" to sail there rather than Fly there, so they get into the fight with the Kraken***). Once they reach the Mind Flayer's Lair, they find hundreds of filthy, unkempt, and emaciated thralls from the Mind Flayers' past possession events who are serving them mindlessly in menial labor and chores. The PC’s also find rooms full of the rotting carcasses of Thralls who have already been fed upon and their brains removed via a hole in the top of their head. And of course, they find Phaequum and Tsazzeng'noth and battle for the future of McCoastalTown!