The Californian Sea Otter, as a species, eats about 30 different types of food found throughout its range. Each individual otter, however, will only eat 3 or 4 of these foods - those it was fed by its mother as a child. It will not eat the others even if failure to do so means it would starve. Maybe other, possibly larger and more dangerous creatures and monsters, have similar habits.
A continent is home to large, leathery flying beasts with a wingspan of over 70ft. Though shy, herbivorous and easily scared, it is possible that an enterprising person could domesticate them. They would be useless in war due to their timidity, but excellent if used for commercial air travel.
A large bamboo like plant grow on a shoreline. Rather than growing round like conventional bamboo, this type of grass is shaped more like celery, and mature stalks just need the ends trimmed for ready made canoes.
There is a race of beings that have endless lifespans. Because of their eternal existence, the only forms of time which they understand are being and non-being. They do not understand words or ideas such as past, future, present, yesterday, today, tommorow, then, now, when, until, ect. They do understand yes, no, live, die, on, off, there, not there, existent, non-existent, ect.
Asclepius' flies are similar in size to the ordinary housefly, but they are white, with crimson eyes (ugly little creatures). Unlike most flies, however, they are not diseased, in fact their remarkable immune system contains agents which tackle even human illnesses. This is the source of their white colouring also. The standard technique for capturing them, to use their juices, is to tempt one onto the palm of one's hand and then to quickly wring your palms, then rub the mush onto the afflicted area. This is not for the squeamish, but has definite healing possibilities.
Swordbiters are parasites. They are long, thin and silver, and digest metal, somewhat like rust monsters, but smaller and more insidious. They resemble stick insects, but when they cling to metal they are very well camouflaged, and one can be biting your sword for a week before you notice it. They cannot be removed by hand, as they are very strong, but if the blade is inserted into fire they will leap off to escape the flames. Sometimes, old treasure hoards are infested with them, and the first glimpse you get of the "glittering" weapons is a pile of rusted swords encrusted with these thin silvery insects.
An insignficant little species, the candlebug (or waxmoth) is a persistent bane for mages and merchants alike. Each the size of a small digit, these little scarabs thrive on wax and burrow up inside candles, ruining them. Sometimes a late-night worker will hear a crack and a sizzle as his candle expires, only to find the half-burned remains of a waxmoth squirming around on his desk. This is very annoying in worlds where candles are expensive...
"Yn these landes, theye do ryde upone greate flowtinge beastes alike as those thate ye fyshermen do calle nawtilus; Ande these beastes, callede 'pyky-pyky' because of ye noises thate the beastes make, are troubelsome ande beastlye mountes, withe fowle temperes." -Telliamed ap Ynris, "Ye Westerne Landes".
(A levitating giant nautilus that makes a noise like "piki-piki" and is thus called a Great Piki-piki.)
A race of beings actually IS invunerable while in adolecence. They age, but cannot be killed. A miniority of the race (1 in 20) does not become invunerable, but rather becomes immortal at some point in thier adolecence, and ceases aging while being vunerable to death in all the normal ways. Another minority (also 1 in 20) Permanatly becomes invunerable after adolecence, but ages twice as fast as the race normally does. There is no known way to test for which of the three traits an individual manifests and the three traits cannot mix, as they are tied to the same gene, as it were.
Inspired by Ria Hawk's winged mushroom picture:
The winged mushrooms (Lerreta Meia) are a species of giant insect indigenous to the leafy areas of Udnalor, Kingdom of the Gnomes. Outwardly they appear much the same as ordinary giant mushrooms, and they graze in the bulbous fungal glades. However, this is merely an elaborate camouflage: the insect beneath is a fungivore and prone to fly off when it encounters another creature. Sometimes gnome farmers mistake them for crop mushrooms. They're in for a surprise when they do.
After particularly intense storm, a green glowing fungi can be found on the trees and plants. Also new monsters seem to be in the region. These storm are obviously bringing these things from other places and depositing them with the wind, rain, and goop upon the land.
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.
Termites, in certain places, make homes that can be eight meters high and only a half meter wide. They are built facing North to South to take advantages of the suns travel, maximum heat in the morning and evening and little in the afternoon. Imagine grassy plains with vertical structions facing a certain direction all over the place. Ambush? Maze? New creature? Larger structures?
If a creature is transformed into another creature (say, a human into a dog), then that creature will become more and more accustomed to the new form until a point is reached where reversing the spell is impossible. A second transformation is possible, but the creature will have to go through the whole process again.
A certain type of demon cannot not be hit by ranged weapons or attacks. Attacks have to be made up close and personal for the damage to mean something. Ranged attacks are to impersonal.
Possibally a way to make the ranged attacks more meaningful would be to coat the arrow head or what not with the shooters blood. Of course, they'd better be a good shot, otherwise they're wasting arrows and already bleeding to boot.
Spells: wizards might have half or no effect, preist might work due to divine intention.
Another real world thing. White tea. Can only be picked two days a year, the two days before the flowers blossom. Could be a similiar plant that...is the deadliest poison known, cure known diseases or psychosis, or a potent herb that just tastes awesome.
Actually a real-world fungus, just heard about it. A fungus that tastes well and all, no ill effects. UNLESS you consume some beverage, even 3 (three) days after eating it. Then you become really sick, pains, vomiting, all the fancy stuff. Was really used to cure alcoholism. May be a joke or to make sure the heroes spend their time focused on the mission.
An ancient, psuedo-immortal race has been manipulating something important (politics, religion, economics, etc.) for centuries. Hardly anyone is aware of them, let alone their goals.
The ochre sands stretch for miles around. Something kicks up the dust. It's a yak. A desert-yak. It ambles slowly, nuzzling the ground for the low-growing shrubs. The ranger freezes. "Stay very still," he warns. "Don't move at all."
"What is it?" you ask, breathlessly.
"It's the most dangerous creature in the whole Ocadian desert. And it's about to eat that yak..."
The cliff-hunters ride sheer-stalkers vertically down the cliff faces to reach the nests of birds and steal their eggs for sport. Sheer-stalkers are vicious agile lizards about the size of large komodo dragons. They must be muzzled and harnessed, but even so there have been some nasty incidents...
Once every decade on the eve of St. Poskov's Day during mid-winter, the coastal city of Tiyabon experiences a horrific event. Quool's Tide rolls in, depositing hundreds of bloated, fish-eaten corpses upon the pebbly shores of Tiyabon's wide bay. This singularity is to this day unexplained, though countless theories abound. It is said for example, that these corpses are not eaten by the myriad fish of the seas completely, due to the fear all creatures of the seas hold for Quool.
Named for Quool, a terrible, antediluvian god of seas and storms, who no longer exists for he has no worshipers, the Tide chokes the beaches and surf with the countless rotting bodies of those who had perished at sea in a violent way.
Almost immediately, the lifeless corpses are fed upon by crabs, gulls, and worse things that await the horrid feast. The townsfolk let nature take it course with disinterested disgust, though lately some enterprising adventurers have taken to searching along the beaches of flesh for former deceased companions, with intentions of raising them again!
Surprisingly no undead ever rise from among the many corpses. This is also a mystery.