Roll 1d20 for Basic Sewer Encounter. If you roll a 20 then roll on moderate difficulty table.
Basic Sewer Encounters
1d20 (how many encountered)
1. Party of Homeless People (2 - 5)
2. Thugs (2-6).
3. Plague of Rats (10 - 100)
4. Clutch of Chokers (3 - 8)
5. Ochre Jelly
6. Pack of Ghouls (3 - 5)
7, Brood of Giant Leeches (3 - 6)
8. Pair of Ooze Mephits
9. Pack of Wererats (5 - 10)
10. Tribe of Morlocks (7 - 18)
11. Pack of Dire Rats (2 - 20)
12. Corpse Infested with Rot Grubs
13. Circular Chamber with Whirlpool at the center.
14. Colony of Giant Centipedes (3 - 6)
15. Rat Swarm
16. Patch of Green Slime
18. Cluster of Gricks ( 2 - 5)
19. Cockroach Swarm
20. Roll 1d10 on Moderate Difficult Table
Moderate Sewer Encounters
1. Pair of Mud Elementals
2. Dire Crocodile
3. Gang of Dark Creepers ( 3 - 6) with Dark Stalker Leader
4. Coven of Green Hags
5. Gibbering Mouther
7. Shambling Mound infused with waste.
8. Grove of Violet Fungus
10. Cabal of Skum (20 - 30) plus Aboleth Master
20 Adventure Seeds
1. Scholar is seeking adventurers to kidnap a Morlock. He wants to study how the Morlocks were created from degenerate human stock.
2. The King of the Beggars. An intellect devourer has killed the most influential beggar and has taken his place atop the Beggars society. He directed them to venture forth at night stealing objects he needs for a creation.
3. A lost catacomb has recently been discovered in the sewers. The city founders were laid to rest there. It has been bricked off for centuries. The catacombs are rumored to be infested with wights.
4. The architect of the sewers many centuries ago used to bury his laborers in the stone walls. Few dare enter the system for fear the dead with seek vengeance upon them.
5. A tribe of wererats are trying to grow their numbers. People have been attacked throughout the city and infected with lycanthropy.
6. There a secret Under Market of illicit goods beneath the city.
7. A serial murderer has recently escaped confinement. He is rumored to have fled into the sewers to evade the authorities.
8. The resident quarter has been infested with cockroaches. Way more cockroaches then normal. They have been dragging large amount of refuse back into the sewers. Moustrous Giant Cockroaches have quite an appetite. The group is paid to exterminate the infestation.
9. People are being mugged in the streets. Instead of taking their purses they have had their hands amputated. The hands are being delivered to a necromancers lair beneath the city. He has created an army of crawling hands. No one know for what purpose.
10. A recently slayed tribe of degenerate Ogres are found in the sewers. Giant festering maggots feast on their bodies. What could have wiped out a whole tribe of ogres?
11. The group stumbles upon a crypt in the sewers. Its guardian is a Crypt Thing who teleports them into the den of a Dire Crocodile.
12. You discovered in a side passage an abandoned laboratory with a partially created Flesh Golem.
13. A homeless man recently found a jester outfit. In his deranged state he has been staging tea parties in the sewer system. Problem is all his guest end up dying.
14. An eccentric Noble is building vaults in the sewer. Claims the end is
15. The thieves guidemaster has recently passed away. Rumor has it he keep his hoard of treasure in a secret stash located in the sewers. The rush is on to find the hoard before rivals get to it.
16. After a night of drinking the group hears screams coming from outside the pub. A woman tells them that something emerge from the sewer grate and kidnap her husband.
18. The sheriff wants the group to investigate a smuggling operations located beneath the city. A group of illicit traders have been smuggling powerful drugs from the Underdark. They have setup storage depots throughout the sewers.
19. Swarms of Rats are pouring out of the sewers. Something has disturb their nest. Why are rats leaving the sewer? What could possible scare them way?
20. A Worm that Walks has united the morlocks, mongrelman, and wererat tribes of the sewers. He plans on sacking the city and turning its residents into slaves. First he plans on attacking strategic locations throughout the city to sow fear and panic.