Imagine a tribe of nomads where all the males have the blessing of being were-stallions. The tribe would not need to have ordinary horses to move around, all mounted warriors would be female and a curious custom could be that when a couple gets married, the girl rides her chosen to the altar.
A character who is undergoing changes of personality (like buying off mental disadvantages - flaws - or changing alignment) might confront personifications of aspects of his personality in dreams: a griffon representing the courage he needs to face a terrible foe, or a satyr standing for the lecherousness a warrior must overcome to be admitted to an order of knights who must uphold vows of chastity.
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...
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...
Sessiliths (name based on the word sessile) are gargoyle-type creatures which are stationary, attached to the stone of whichever foundation they are bound to. Though they can move their extremities and limbs they are unable to move away from their particular perch. In lieu of swooping down and attacking like their mobile cousins the gargoyles proper, sessiliths are equipped with their own brand of mischief. The creatures are all able to verbalize and thus usually hurl vile insults and curses upon passersby. The cumulative effects of dozens of sessiliths cursing, screaming, and speaking in tongues, can have an effect of temporary confusion (or even discord) in those forced to listen to the shrieking stone gremlins.
Additionally, most possess the ability to "spout" or spit forth various undesirable projections, such as tar, boiling water, or even acid. While they can usually be avoided easily enough or even destroyed (their "bodies" feature the same defenses as gargoyles), sessiliths are usually placed in such a way as to hinder all trespassers and interlopers, narrow corridors, claustrophobic tunnels and other related "gauntlets", where they cannot be easily avoided. Like gargoyles, sessiliths come in all sorts of grotesque shapes and sizes, though they tend to resemble tiny horned devils, demonic amphibians, or simply distorted faces and heads, more often than not.