Consider the idea of spontaneous genesis of life, as used to be belived. What strange kinds of life might arise from modern substances? What kind of vermin would a landfill produce, or an oil spill on the ocean?
Throw in a handful of random customs - like women or men of a certain level of society being required to wear a veil or a pendant of some type.
Magic is the lifeforce of all living creatures, and it is from it that all life is made - in areas with lots of undead, magic might actually be missing or weak, which puts a whole new spin on how dangerous the undead are. Even simple zombies can be troublesome if you're relying on mages and you hit a pocket of undead making a low-magic zone...
How about a dragon how cheerfully rules over a kingdom; his people all know him for what he is, and dragons are looked upon as wise and benevolent creatures. Dragonslayers from other kingdoms coming to free it from 'tyranny' are likely to get beaten to death by peasants with cast iron skillets.
A demon who isn't some hideous creature bent on consuming souls, bu is, in fact, a likable chap who enjoys having pleasant chats with people - trying to talk them into becoming his servants.
Someone needs the blood of a dragon, given willingly, to make a rare potion. Guess who gets hired to sweet-talk a dragon into giving up some highly powerful blood?
Faerie foods with unusual effects. Like faerie sausages that turn the eaters into wiener dogs, faerie wines that make the drinker whiny, etc. There's a table in Palladium Fantasy RPG which has a table of ideas.
These rare, fist-sized spiders do not make webs, but rather excrete secretions which harden upon contact with air. These "droppings" resemble barley-sized spider eggs, or even lustrous pearls, once the slime coating them, dries up. In fact, dried Pearl Spider "drops" are indistinguishable from the marine varieties produced by mollusks, and hence of identical value on the open market!
Several centuries ago, they were studied by naturalists, and several observations were made. Firstly, was that these spiders "lay" these pearls for no apparent or discernible "natural" reason, and secondly, the naturalists had discovered that the more these spiders ate or were fed--and they were true omnivores--the larger the spider pearls came out.
A cottage industry began. Enterprising merchants hunted and collected these creatures across the lands, erecting spider-farms for the manufacture of Spider Pearls. It wasn't long before someone got the idea to force-feed the spiders, ala foie gras geese, and soon, the fattened spiders began pooping out pearls of great size! (relatively speaking). The regular pearl market came to disarray, and prices and value fluctuated wildly.
[b]Plothook[/b] The Mermen Mercantile Alliance hires the party to eradicate all terrestrial Pearl Spider Farms!