What monsters would live in a sewer?

[Yqatuba]

Other than the obvious (rats and wererats). I could see oozes and maybe some vermin surviving in a sewer. I also think a young black dragon having a lair there wouldn't be that far fetched (as the usually live in swamps, they probably don't mind bad smells much.)

[Particular Jones]

Yqatuba wrote:

Other than the obvious (rats and wererats). I could see oozes and maybe some vermin surviving in a sewer. I also think a young black dragon having a lair there wouldn't be that far fetched (as the usually live in swamps, they probably don't mind bad smells much.)

Otyugh, Orcs, Troglodytes, and Blights. If their is enough access to water Saughin. Blights are another though if you sue them make sure the party is a decent level or it will be a TPK

[SheepishEidolon]

Derros. Bugbears. Ghouls. And if you want even more horror: Humans.

[mardaddy]

Mongrelmen, sewer goblins, goblin snakes, mites and all their insect affectations, skulks, just about anything that wants to or could live on the "fringe" of, and feeding off of, scraps of civilization.

[PCScipio]

As previously mentioned, Otyughs are an obvious choice.

[Darigaaz the Igniter]

"mud" elementals

[Mudfoot]

Giant mutant alligators.

[Mark Hoover 330]

Despite the pollution of the water, there are rare instances where a pool forms with silt deposited by storm runoff. Add a sewer grate that lets some sunlight in, you might have an Assassin Vine or a group of Leshys. The damp and darkness is also a great place for Hazards like Brown Mold, Green Slime and the like.

I could imagine, as a twist, groups of urban Sprites protecting animals living in the sewers. Said animals would be those loose creatures that might also inhabit the fringes of a fantasy city: rats, yes, but also cats, dogs, bats, mice, and so on.

Speaking of the fey: Gremlins, Nuckelavees and Morgodeae are good candidates for the sewers. A Bogeyman stalking the streets above could use the sewers as their lair. Weirdly, there's a few fey who could make some creepy encounters down there.

Finally... aberrations. Seriously, they're such good, solid brutes for an all-out brawl. If the PCs are low level, throwing a Choker in to grab one of them in the back of the marching order (since they have to walk single file) and having it duck into a pipe with the victim; at mid level making that pipe a mimic or gibbering mouther; throw a Chuul in a cistern or central pool of churning water; at upper levels there's a variety of nagas you could use to ruin the PCs' day.

I feel like aberrations get used in the APs but often get left out of forum posts about good monsters to use for "X" because they're usually just mindless or alien predator types. Thing is, sometimes that's what you WANT in your encounter. A lot of aberrant monsters have Climb speeds or can be aquatic, they have brutal natural attacks, and they'd likely be shunned by the daylight world.

Oh, and one honorable mention for a moody, low-level brute monster: a Thawn. They're a CR 2 alternative to an ogre. They're tragic flaw is that they're reviled (may become Sickened) by their own reflection or looking upon other Thawns. Other than that they're Large humanoids who blend in real well with mud and refuse.

[VoodistMonk]

Leech Swarms with the Aerial template. Lol.

Definitely a Tendriculos.

Ceratoidi, reskinned for sewer water instead of salt water. They make great TWF builds with a few class levels.

Bats, spiders, rats, anything insect/bug/vermin related.

Anything mutated or formless... Aberrations and such.

Gotta have a Killer Croc crocodile-man.

[Mark Hoover 330]

Take 4 Lizardfolk NPCs. Remove their natural attacks for increasing their Natural Armor bonus; explain this away as a hard, outer shell covering their full back. Now give them the appropriate levels of the Ninja class. Now give them names from the Itallian Renaissance painters.

If you DO take this suggestion, do NOT give these NPCs: a catchy theme song, pizza, skateboards, or catchphrases involving some permutation of the word "radical." For inspiration, seek out the source works of master comic creators Kevin Eastman and Peter Laird in the original black and white.

For added depth, giving these four NPCs a fifth, mentor-type built from a Ratfolk is not out of the question.

[TxSam88]

A smart town would have purposely put gelatinous cubes in the sewer to keep it clean and clear. if so, there shouldn't be much else.

[Yqatuba]

VoodistMonk wrote:

Ceratoidi, reskinned for sewer water instead of salt water. They make great TWF builds with a few class levels.

.

What's TWF?

[avr]

Two Weapon Fighting, Yqatuba.

"Exist" might be a better word than "live", but undead in a sewer is an old trope. Possibly even intentionally raised in order to keep down the populations of some of the above...

[Scott Wilhelm]

Mudfoot wrote:

Giant mutant alligators.

Alligators? That's definitely a myth. We have lobsters....

[Scott Wilhelm]

VoodistMonk wrote:

Leech Swarms with the Aerial template. Lol.

Lots of kinds of Swarms.

[Mudfoot]

As a result of unnatural alchemical effluent from the local academy, the sewer itself has become sentient, and resentful of the people above pouring filth into it without a moment's care. It can move to a small extent to squeeze the impurities through or to block the inlet drains, and has ways to communicate with those living in it.

It's turned a gang of street thieves who had habitually used the sewer as a hideout into deranged cultists; they're now stealing building materials, murdering alchemists and otherwise working to aid the sewer's bizarre end goal...whatever that is.

[VoodistMonk]

The Golgothan $#!+ Demon from Dogma.

[Ryze Kuja]

Honestly you can put anything anywhere as long as you have a backstory for “why” it’s there. But if you’re just asking for generic sewer monsters, Otyughs, oozes, and gelatinous cubes are probably the most stereotypical sewer monsters in the book. Swarms of just about anything also fit.

Depending on how big your sewer is, and how big the city is above it, you can have lots of other stuff going on too. A lot of major cities have been built on top of themselves several times over as well, so your “sewer” might actually be a bit of a history lesson because the party will be venturing into 2 or even 5 layers of old city, spanning hundreds or even thousands of years. So this can attract Witch Covens, priests seeking privacy for performing rituals to evil gods, currently-homeless Rogue guilds, enemy spies from a neighboring city-state who are seeking a hidden path for their forces to infiltrate the city above, even Druids who are sick of humanity and are growing a festering farm of “Deathshrooms” to wipe out the city.

[VoodistMonk]

Where, and into what environment, does the sewer drain?

Is the waste of civilization poisoning a lake? A marsh? The ocean?

Are there any halfway competent Druids or Fey in this area that may have a problem with this aforementioned poisoning of nature?

Since it's literally cr@p, the sewers are probably all but forgotten about by the general population above... the drain into the XXX is not guarded or even maintained. That allows the Druid/Fey to weaponize this poisoned and perverted part of nature, and turn it back into the sewers below the city.

Here the Druid/Fey builds up this biological abomination, allowing the twisted and diseased plants/molds/fungi to fester and multiply. Over time, the entire sewer system is filled with vines, roots, moss, and mold... the damp air thick with spores.

When the time is right, and the ritual complete, the plants will erupt through the culverts and reclaim the city...

[Yqatuba]

VoodistMonk wrote:

The Golgothan $#!+ Demon from Dogma.

Does a demon like this already exist? I guess you could use an omox and reflavor it (and give it the stench ability).

[Tim Emrick]

Kobolds (they're an entire tribe of "Sewer Dragons" in one Society scenario).

Homeless people of all types (it's shelter, and they're rarely bothered by authorities)

Anyone who needs to avoid public scrutiny of their foul deeds: cultists, mad scientists, smugglers, assassins, eco-terrorist druids, etc.

Drow, morlocks, medusas, and other monstrous races that would be shot on sight on the surface, whether rightfully or not. (In Green Ronin's Freeport setting, a disturbing number of serpent people hide in the Undercity, of which the sewer system forms a major part.)

Animals and other monsters who escaped their owners/handlers and somehow thrived underground (crocodiles and giants snakes for real-world urban legends; but really, any weird monster that likes the dark and/or water, and that could be deadly to its owner if not properly controlled)

Water spirits corrupted by urban pollution (corrupted fey naiads, disease-ridden ooze mephits, etc.)

Watch patrols that drew the short straw and had to investigate trouble in the sewers. (Freeport has an entire Sewer Patrol organization devoted to stopping threats before they reach the surface. It's one of the most dangerous, and least prestigious, law enforcement posts in the city.)

[Goth Guru]

Racoons.The giant, dire, varieties are effectively bears.
Racoon Dogs are powerful shapeshifters that play a major part in many Japanese legends. As they can take the form of children, halflings, and of course dogs, they may lead adventurers right to their enemies.

[Mudfoot]

Given the material present in a sewer, there may be methane pockets building up if it's not well ventilated. If the PCs bring torches, lanterns or fire magic, the results might be quite unfortunate.