What sorts of worlds could you create if you took all the fantastic monsters out of the game and allowed only humans, animals that live right now, and ten singular varieties of monster..."
Given that I do not run humanocentric campaigns and tend to include undersea elements and hags in most of my plots, it might be interesting to narrow it down to the following choices. Most of the choices would be available for players, as well.
Human: NPC use only
1. Sea elf: a touch of the fey for the adventure
2. Locathah: In my games locathah are hermaphroditic and are placed into a caste system based on the colors they develop as they mature.
3. Merfolk: a classic; the "core race" of the campaign
4. "Awakened": since we acknowledged flora and fauna, I would add the means by which animals and some plant-life could attain sentience and be used as PCs and NPCs
5. Lycanthrope, wereshark: Though technically not a race, this would add the element of lycanthropy. As well as adding the means to explore the mysterious and hazardous world above the surface of the sea.
6. Shellycoat (aquatic greenhag): If I had to narrow it down to one hag, then the shellycoat, as I envision her, seems to fit the bill.
7. Aboleth: an element of the pseudonatural for the adventure.
8. Lacedon: an element of the undead for the game. Rules for advancement a la Libris Mortis would apply.
9. Merrow: sea ogres
10. Scrag: sea trolls
From these beasties one could also derive half-elves, garibaldi (a human/locathah crossbreed of my own design), sea hags (a shellycoat-merrow hybrid in my games), shoal hags (a shellycoat-scrag hybrid in my games) opinaku (similar to sea kin, the offspring of human weresharks and sea elves, in my games), skum (creation of the aboleth), half-merrow, and half-scrag.
