Selamat Datang!
Mmm... mangrove swamps, my man, mangrove swamps.
The roots of these trees jut upwards into the water, but can't be seen very easily in bad light, and the foliage around them just makes things worse. They can be very sharp and painful - falling down on them can literally kill you, if you're not careful, and at the very least do a nasty entangle/caltrop/spear effect.
On the plus side, these roots do provide a useful purpose - they can be used as a sort of rough walk-way to navigate areas that are otherwise impassable. for those who can climb and balance on them - it's not that high a DC, around 5 or so for most, but it does mean that PCs who wear heavy armour will be sorta screwed, and the Climb/ Balance rules really slow down and weaken a PC's defence.
In the swamps i used to work near, there're interesting critters inside there - met a few monitor lizards (really smelly buggers, they stink to high heaven! but when they run, their legs go into little barreling wheels of locomotion haha, like a cartoon - it's incredible how quick they are!), a few fat pythons, and lots of birds. There' re a bunch of wild cuckatoos in the swamp, around 13 or so of them, colourful chirping cheerful ones, and they serve to eat up quite a lot of bugs. Also, stork-like herons, with long legs like to walk around and eat frogs and snakes...
Also, make good use of poison rules. there're these fruits lying around here in tropical Southeast Asia that we call "Pong Pong", they grow on trees - they look just like largish green apples. Unfortunately, they happen to be utterly, utterly poisonous. Things like leaves, shoots, curare bark, etc... they can be very, very disturbing to the forager who's more used to forests and temperate climes.
Large funky plants and fungi are cool too. The Rafflesia is a large flower-like fungus that stinks of rotting sweet goo, and there're lots of ferns and vines all around. Some of them have medicinal value, and others are poisonous too.
In the caves of Indonesia, near the swampy areas, people harvest Bird's Nest for herbal poultices. The swallows tend to build their nests from a mixture of their own saliva, twigs, and other stuff in caves near swamps or rivers (because of the insects around i think, that form a good easy source of food). It's real hard work cos their nests are placed right on the top of the cave ceilings, and it's really slippery and dark - so it's kinda like a premium expensive item. It's supposed to have curative and anti-venom qualities, for your poor beleaguered adventurers... In real-life, a bowl of bird's nest soup with other herbs can cost up to 10 bucks or so, for the cheaper versions i think.
Pontianaks and Penaggalans are swamp-dwelling undead that're drawn from Malay folklore - heck, tons of folklore in Malay culture are about swamp-dwelling monsters. Penaggalans are flying heads (usually women with long hair, eek!) and their entrails are dripping out behind them from their neck, they fly around and attack people by biting them and strangling them with their guts. OA 3.0 had a version there that could be appropriate. In folklore, they tend to live in tree hollows..
Pontianaks are female vampires who are created when women die in childbirth. They rage against the men who had killed them, and they are bound to frangipani trees, which have little pretty white, sweet-smelling flowers. Whenever you smell a frangipani blossom, it's usually believed that there's a pontianak around... i've had freaky experiences in my own neighbourhood when i walk in the middle of the night on a tree-less bouldevard, with a totally still night sky and then i smell a waft of frangipani. hahaha! they're the traditional bogeymen here..
Other things that are swamp monsters include leeches - i've heard tales of leeches that drain blood and turn their hosts into zombie thralls under their command. the psionics handbook Puppeteer sorta replicates this. There's also a freaky giant demon that looks like a normal man, except his legs are maybe 2, 3 storeys tall? He walks over you with his legs and you get Plane Shifted to Hell, or so i've heard from the old greybeards hehe.
Hope this was helpful!
Yours,
shao
