Maybe have an area of town near a sewer where they encounter a rat king.
"Rat kings involve a number of rats intertwined at their tails, which become stuck together with, for instance, blood, dirt, ice, horse-hair, or feces—or simply knotted. The animals reputedly grow together while joined at the tails."
https://en.wikipedia.org/wiki/Rat_king
View attachment 94464
Maybe take this idea and use the folklore of an actual bundle of rats like this forming a larger rat creature made up of many rats.
Thanks, that's a great idea! I can definitely have this as something found around town, maybe at the Hanging tree where the were-rat's ancestor was lynched. I'll probably have the PC's find it if they go there, and then they can get more information about the folklore from some locals.
May I introduce you to Skavens?
http://warhammerfantasy.wikia.com/wiki/Skaven
They are a warhammer-specific race of rat-people, but they are *awesome* and would work great in a D&D game IMO
http://www.drivethrurpg.com/product...ildren-of-the-Horned-Rat?src=hottest_filtered
I love me some Skaven.

Someday I will use them properly in a campaign. In fact, now that you mention it this adventure could be a prelude to some Skaven-like developments under the auspice of the Horned Rat. I'll have to mull that one over. I have a number of adventure hooks pointing toward the Caverns of Thracia later on, but nothing is set in stone. I had initially dismissed the idea of going full Skaven here, but it could be fun. I'll have to see where the players' interests take them, but I think I'm going to have to include this as a possible lead.
You might also consider introducing plague or famine. An excess of rats tends to come with one or both of the above, and the mention of sickness and hunger in the town above could go a long way toward building the atmosphere. Plus, if the townsfolk are sick and starving it adds a sense of urgency. Maybe have the players overhear a passing comment that if this isn't dealt with soon the town is done for.
I like it. It would be very easy to have sick villagers walking around, and a plague starting to overtake the populace. I think I'll embellish it by having the general rat population increased and much more noticable. Rats appearing where they shouldn't, such as falling out of cupboards, gnawing through sacks of grain in cellars, in the PC's beds in the inn, etc.
When I think rats I think famine, filth and plague. Funny noises of skittering feet in the middle of the night. People with long twitchy faces with pink eyes and greasy hair crawling with fleas. Give them the mannerisms of a rat on top of that - a little hunched, holding their hands up by their chest and rubbing them constantly, etc.
You could also have other minor queues. All the cats in town disappear (have a kid calling out for Whiskers and crying), you see dogs running in terror from something hiding in the alley. You see glowing eyes staring from the darkness that scatter when you approach.
When investigating areas the rats are, there are gnaw marks everywhere. On bones, on floors that were weakened so they collapse when someone larger walks through, tunnels just big enough for a wererat goblin to crawl through.
Hope some of that helps!
Love it! I especially like the idea of the cats disappearing. That's suitably creepy and ominous to really give them the impression that something strange is going on. Also, I really like the ideas of showing the evidence of rats in the mines. The party explored the first few rooms, killing a bunch of normal goblins and then retreating, and when they returned they saw that the corpses had been badly chewed on. I'll play that up some more with showing signs of gnawing on the timbers, maybe a tunnel that has been weakened because the timbers are gnawed so much. I think I'll also just play up the density of the rat population in the mines. They're not a direct threat, but they are ever present, and it can lead to the PC's finding rats in their backpacks, eating their rations, gnawing through straps in armor, etc.
I think my next step is to create a couple of lists of "mood-setting encounters", one for town and one for adventuring. These ideas are all great and will definitely be on the lists!