If mana recovered slowly enough, and mages could pass it on freely between them, the ephemeral force would become a valuable trading commodity on its own.
What if a mage passes his powers on to his firstborn son, and a female mage to her first daughter, leaving the parent POWERLESS? A plain mortal, a sorcerer no longer, all wizardly might gone?
Or: what if a female wizard recieves the power of a mage who sires a child with her? Could lead to promiscuous witches and overly careful mages.
What if cancer is not an ailment if one has a will powerful enough, and knows what do do. What if one using the right techniques could control it and use it to become immortal, or to grow into something else?
Pick up a pathology/microbiology book, and add the diseases/syndroms to your game. Your players will freak out.
Coughed at? Diphteria. or tuberculosis?
Drunk from a muddy stream? Or just walked through? Well, let us introduce you to schistosomiasis...
Hit by a stream of energy? Too moch mana is ust like too much radioactivity - perhaps all mages could develop cancer early if too powerful...
Elves are not actually aloof. They are actually extremely family-based and insular, and often intermarry inside their families, making them uncomfortable around those not of their family. Therefore, they shield themselves behind pretended aloofness and coldness until they are comfortable in others' company.
The PCs traveling along the road/path/trail begin to hear a low droning sound. As they approach they find their path obstructed by hundred of thousands of droning insects. Locusts swarm though the air, feasting on the grass and plants. Passage will be slowed, but the insects pose no threat to the party, aside from being crunchy and disgusting underfoot, climbing into pouches and eating exposed food goods.
Expansion from the Horse Brass item: Specific Armor charms.
Cooling Touch Charm: protects horse against extreme heat, and fire, magical and mundane
Jove's Favor: tin charm shaped by a lightning bolt that protects a horse primarily from natural lightning, but also potentially from lightning based attacks. In real life, lightning kills quite a few horses and cattle a year.
Hermes' Blessing: gold charm that grants the horse magic resistance, and perhaps immunity to cantrip level magics.
Vulcan's Steed: This large iron charm in epic fashion renders the steed invulnerable to iron weapons. Such things clatter off of the animal's hide like twigs.
You wake in a pub and see that it's full of were creatures, and they're all staring at you with a scared look on their faces. As you continue on into the pub you look at your arm. You notice that your arm is covered in thick brown hair. As you continue on into the pub you look in a mirror, and staring back at you is a 7 foot werebear. As you continue into the pub people start to shy away form you. Once you go the bar you ask the weretigress that's the bartender and begin to ask her why everyone is shying away from you, and she begins ro tell you why.
The king's palace is destroyed by a falling star, which detonates like a nuclear bomb in the center of the city. When the inhabitants grow brave enough to investigate the ruins of the palace, they find a new ruler, one from beyond the stars, emerging from the meteor.
Animals have parasites and diseases, so do plants, there are even bacteria that cann dissolve oil spills or plastic or what have you - why couldn't there be a disease living off magic - a magic item could be infected, losing power and speading the plague to other equipment it contacts, while a magic user would slowly lose his powers and contaminate all he works with or casts a spell at...
Small identical wooden or metal discs with a strange pattern engraved upon them (do not appear to be coinage). The discs can be found all over the continent; a farmer typically overturns several dozen when ploughing a field. Though they are unnaturally hard to break, they have no known use and are widely used as good-luck charms: almost all households would have them on the doors and on mantle pieces; many people carry one or more on them, bound on to a belt, necklace or sewn on to their clothes.
A party of adventurers walk along late on an open plain, on a moonless night. Abruptly, War screams, the clanging of metal and death-cries are heard. It is an open plain, and nothing is seen, but the sound of a huge battle is all about them. The sounds continue for a half hour before stopping as suddenly as they started. What was it? Perhaps the ghouls of a long-gone battle, reliving their unfortunate last memories...
Arkths or Ravagers: These are large landbound crablike creatures about the size of Grizzly Bears. They live partially in the astreal plane. Their food is magic. They can sense it at huge distances. Since spells and such are hard to eat (being in motion) and magical places are the equivalent of a sea of krill to them, they are looking for magic stashed in concrete places. Their primary food source is magic items, alchemical potions, and enchantments. They do a pretty good job of mangling/ eating the physical aspect of said items in the process of chowing down. These things will be the bane of dungeons everywhere, as they will slowly eat away much of the treasure (and the magical traps... so it can be advantagous to follow these things). Note: They will attack people with highly magical natures (i.e. high magic powers). They will probably kill the person in the process of sucking out the power.
A secret MLM (pyramid) company that offers eternal life, but in fact it transfers the life forces of its members to those position "above". If you get high enough, (meaning you get enough new members) you start to enjoy the benefits. Maybe a willing sacrifice is much more effective for the transfer. But no one says, that a suddenly unwilling member, threatening to tell the authorities, may not loose it involuntarily... thus start people to vanish, and aged corpses are deposited somewhere safe.
These goatlike animals, who have shaggy coats and layers of scales, are good retainers of water. They are close relatives of Suppoki. Their meat is considered a delicacy in many countries.
No desert tribesman leaves his settlement without a Rakda.
These creatures are desert animals that are much like huge, quadripedal sloths. They have a hide made of heavy scales to keep out gritting sand, and over that, a thick coat of fur.
During sandstorms, and when they sleep, Suppoki bed down in the sand, covering themselves up until they are miniature dunes.
Suppoki derive what sustenance they can from water sinks, dew, and underground insects.
Suppoki are often ridden by desert tribesmen. They are stubborn and slow, but are often the difference between life and death out on the sands.
As the PCs travel the road, right after a bend they hear a sharp whistle and call: "Heeey, not so lazy, move your asses!" It is a large man that calls, and there are unwilling workers that listen. A small company, 10-15 men work on the road, push boulders aside, dig up roots from under the road, etc. The large man that shouted turns to you, smiles fast and mutters something under his breath, sounds like cursing some lazy worker. "Where does the road bring you from, travellers?" And does a little small-talk.
And what is really happening? A group of bandits is 'adapting' the road for shady purposes. The road will not be wider, but tighter, with enough cover around (and a few traps perhaps), and will become an ideal spot for ambushing travellers or entire caravans. The bandit leader wants them all to appear harmless. The 'lazy worker' he cursed was actually a guard that should give warning before any travellers come around (fallen asleep). Not surprisingly, the boss may decide for an ambush even now.
Telepathically linked twins that have the ability to switch places. Literally. They've learned to exploit this 'tag-team' throughly.
In a certain nation, no-one except the Emperor is allowed to have a name. Therefore, the people give themselves pseudo-names called "callings". Examples of callings: A family is known as the Red Sparrow family. The father is called Swooping Red Sparrow. The wife is Bright Red Sparrow Blue Lizard because she was called Bright Blue Lizard before marriage. Their daughter, until she becomes an adult, is Daughter of Red Sparrow. Their sons are Eldest Son of Red Sparrow and Younger Son of Red Sparrow.
What if some crazy wizard created an artifact that empowered rodents that touched it with one random supernatural power? Preferly right out of the pages of your favorite four-color. (But only one power!) This item does not convey any sort of intelligence boost.
The PCs are stuck in a town with a strict peace policy, the tiniest scuffle can land you years in prison. The town also happens to be a tourist haven, so inn-prices have skyrocketed. The only way the PCs can rest is if they splurge on a room, with their enemy.