Bay 12 Games Forum

I recommend David Arora's Mushrooms Demystified. It's one of the most detailed books about mushrooms, weighing in at 900+ pages. containing over 2000 species and over 800 photos. It's somewhat out of date taxonomically, but the lamens names can easily be tracked down. Further, it only applies to North American variants and strains: even members of the same species can be varying in flavour and perhaps toxicity based on the soil and air they grow in. Here are some which are deemed poisonous or unsavoury, but non-lethal according to his book.
Flat-Top Agaricus: vomiting and diarrhea; metallic taste.
Cortinarii: edible variants are typically extremely bitter, and many are incredibly slimy.
Poison Pie: mild to severe gastrointestinal distress.
Bitter Hedgehog: bitterness deems it inedible.
Emetic Russula; The Sickener: induces vomiting, very acrid in taste.

Further, while searching the book, I found one interesting specimen. Crampballs, which Arora says could be used as a substitute for charcoal. I don't know if you could implement it just as that. They're supposedly quite common in forests.

Some more ideas.
Animals:
Equids: Onager, Kiang, (African) Wild Ass and Przewalski's Horse. Hinnies as a female counterpart to the mule, though sterile still.
Canines: Maned Wolf, (African) Painted Wolf, and Feral Dogs. Feral Dogs all have the [CRAZED] tag, preventing safe domestication.
Primatomorpha: (Various Species of) Lemurs, Drills and Colugos. Colugos are frugivorous, flying vermin who live in mangrove swamps and tropical forests.
Rodents: Springhares and Jerboas. Vermin which are functionally similar, only with different habitats: Springhares live in tropical savanas, grasslands and shrublands, while Jerboas live in deserts. I don't know if possible, but perhaps give the giant and man variants of them physical attributes which promote jumping.

Plants:
Woody Cacti: Giant Club and Cardón. Giant Clubs produce un-brewable fruit.
Fruit Cacti: Pitaya and Peyote. Grows in deserts and can be farmed aboveground. Both brewable. Peyote and derived food/drink cause dizziness and good feelings.
Trees: Buckthorn. Buckthorn is a small, temperate broadleaf tree that produces brewable berries. Buckthorn berries and derived food/drink cause nausea as well as stomach and gut pain.
Flowers: Datura. Datura can be harvested from rainforests and grown aboveground. Datura and derived food will make the consumer become [CRAZED].

One of my dwarves assumed the position of king. So, I set about building him his quarters, dining room, etc. At some point, he became stressed from his work-in-progress quarters, and my fortress of 7 had become heavily burdened by building it and meeting his demands for tower shields and sledgehammers. So, I decided to dispose of him. I shut him in his quarters, and forbade entrance. Further, I had two of my miner-masons build a brick wall in front of the doorway. The king himself was a miner-mason, so I assigned him his original labour, and had him dig into the water-chamber. Soon after, another assumed the position, and I resolved to end this line of monarchs in the same fashion, by flooding the fortress.

Hiring of outside help in dwarf fortress is incredibly sporadic and is done through the tavern, and even when it does happen you can only hire mercenaries and performers. You could make some of that caste based, but having 'Mountain Gnomes' born from shrubland gnomes would get kinda weird, that and you wouldn't actually hire them. I didn't really know that there were lathes made specifically for wood shaping, so I guess I'm okay with that. I don't really feel like a human sized wizard really fits into the feel of this mod, but I don't see why a gnome sized wizard caste couldn't happen. I kinda think leprechauns should be their own civ, but you gave a pretty reasonable reason for them to be a caste. Also, maybe we could give vanilla mountain gnomes an overhaul to give them their own civ?

By hire, I mean like pets. That's effectively what the Worker Gnomes would be: a pet with three castes, two male and one female, that is set up so it can perform tasks. Other mods have similar such creatures, and even standard DF has the Gremlin mayors. In general, I think Shrubland Gnomes should be the more fanciful player race, which is why I suggested them being able to birth physically-human wizards, as wizards do oft come from fairies and other sprites like Gnomes. Leprechauns don't have to be strictly the Gnome-born variant, as the Gnome-born variant is more a mischief spirit than an actual creature, so it might have a maxage of 1-2 years to prevent Leprechauns from going around in Gnome society. Perhaps Leprechaun isn't the best word for it, but I do like the image of Gnome babies being snatched away in the womb and replaced with clawed gold-snatchers sent to maim and murder. I like the dynamic that is created by there being four variants of Gnomes, with two wild Gnomes who prefer to frolic in the hills or dance in the wormy mounds, and two civilized Gnomes that often contact and make use of their older, savage kin.

Just tested some quick, patchwork Helper Gnomes. The Mountain Gnome traits make them clutch barrels upon going for a drink, disabling their productivity for some time. They begin with skill in poetry, singing, instrumentalism and dance, as well as having some poems learned by default. They need to sleep, drink, and I assume eat. You can conscript them into the military, assign rooms to them, and place them into noble positions. All I've done was clone the Mountain Gnome and give it the domestic tokens, so their behaviour can, and should be tweaked around a bit. Very interesting though, to say the least.
EDIT: They seem to clutch everything, including but not limited to: stones, eggs, beer, etc.

Some things to differentiate Redcaps and Dwarves.
1. Redcaps have four castes. Browncap, Bluecap, Greencap and Redcap. Browncap have innate novice skill with axes, fighting and woodcutting. Bluecaps have innate adequate mining skill due to "being lead" by the aforementioned blue caps. Greencaps have innate competent plant gathering skill and can release a cloud of nausea-causing gas. Redcaps have no innate skill.
2. Redcaps, being tower-builders, can produce a higher amount of stone blocks. The Stonecutter workshop takes one rock and makes 6 blocks.
3. There is only one noble, the foreman. The foreman serves the purpose of manager, expedition leader and broker. He requires meager quarters and a meager office.
4. Redcaps can produce cheap wooden weapons at a Lathe, allowing for quick but poor militias.
5. No strange moods, meaning Redcaps will have to loot for artifacts.
6. Redcaps are predisposed to anger and against depression, anxiety and stress.
7. If possible: Redcaps will have good thoughts if they get caught in the rain or see a non-Redcap die/dead.

I reckon Boggart-made sour milk would be alcoholic. Maybe with a brewing reaction that turns milk into alcohol.

EDIT: Some ideas for Wee Folk.

Gully Dwarves, inspired by the Gully Dwarves from the Dragonlance setting from Dungeons and Dragons.

Despite their name, their stature and their beards, Gully Dwarves are not 'true' Dwarves. They're said to be a cross between Gnomes and Dwarves, or Gnomes and Humans. Whatever the case, Gully Dwarves are far separated from the fortress dwelling, metal smelting, beer drinking Dwarves we know. Gully Dwarves can be summarized in a single word: poverty. Gully Dwarves live in tribal communities situated within ruins, swamps and caves. They wear disheveled, ancient clothing passed down generation from generation. Gully Dwarves value tradition, merriment, hard work, family and peace above all else. They despise law and decorum. They will gladly eat sapient creatures, make trophies of all creatures, and steal from one another. However, they despise murder, torture, lying and oath-breaking. Only the smartest of Gully Dwarves can count higher than one, and those who can do so are regarded as wizards in Gully Dwarf culture. Gully Dwarves are known for sending thieves to fortresses to steal, much like Kobolds. Gully Dwarves have no gods, and instead worship their ancestors. Gully Dwarves use wooden clubs and thrown rocks as weapons. Despite their poverty, stupidity, lack of metal and their criminal proclivities, Gully Dwarves manage to survive due to their high fertility and their relatively short childhood. Gully wives are able to produce litters of four to eight children, children who mature at the age of eight.

Floresiensans, inspired partly by homo floresiensis.

Floresiensans are violent, Dwarf-height tribal people who live in tropical locations. They value martial prowess, family, tradition, cooperation, and nature. They despise peace above all. They allow all things, from murder to cannibalism. Floresiensans use wooden, stone and bone javelins, axes, spears and clubs as their weapons. They are known for having domestic orangutans, chimpanzees, gibbons and other primates. In addition, they breed a special species of primate. Arborpithecii are tame, semi-intelligent apes which the Floresiensans use as work and war animals. An adult arborpithecus stands at the same height as a Dwarven child, but possesses the strength of an ox.

An evil, slow-moving blob-type creature protected by a layer of sponge. Contained beneath the sponge and the flesh is a perfectly normal humanoid skeleton. Its main attack would be through toxic gases it emits which cause paralysis and necrosis of the brain, allowing it to roll over and crush its victims.