I just did some research on redcaps, and wow, they're more brutal than I thought they would be. Apparently they soak their red caps in the blood of their enemies. If you can somehow work out a mechanic to soak items in blood that would be a great feature. They also have long teeth and claws literally described of being that of an eagle. In addition to their red caps they also use iron boots and pikestaffs as weapons. The pikestaff shouldn't be too hard, but can you use footwear as a weapon in dwarf fortress? Maybe you could just have a handheld weapon called 'iron boot' that when used it says 'redcap stomps (enemy) in the (body part) with his +iron boot+'. They are said to hurl large stones down at people who pass by, you could either make a stone hurling weapon or give them an interaction that allows them to fire a glob of (throw) a rock. Having a people with a natural range attack is always a lot more unique of an experience than you'd think it would be. If you hold up a cross and read certain scriptures they'll disappear in a puff of flame and only leave a tooth. Maybe instead of leaving a corpse you could have them only leave a tooth? I don't know how much that would do for game play, but it would be an interesting flavor thing. They're also really strong for their size. They also make really loud grinding noises to piss people off, maybe you could give them a sound based interaction that causes people who hear it be more prone to rage. They soak the foundation stones of their castles in human blood, maybe they could have a unique weapon material 'blood soaked/infused stone' where they take a corpse or an animal and combine it with a stone in an interaction to make a decent weapon material. They capture people for sacrifice, I'm sure there's a lot of sacrifice stuff you could do. I can't find what they exactly sacrifice to, but they sacrifice to something. There's also the possibility to create castes for the redcaps because they have a lot of different regional depictions. Perthshire redcaps are more benign and are even said to bring good luck to those who hear them, and the kabouter (I could do more research on them specifically if you like the caste idea) is almost a completely different third thing. Apparently the redcaps also have a tendency to wrap people in lead before boiling them alive, maybe a molten lead weapon or something?
For future wee folk I have also found:
trooping fairies (there's a good deal of fairies attached to this one)
bluecaps
far darrig
nain rouge
Saci (this one's really weird when you think about it too much)
pukwudgie
