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...
As far as everyone knows, the Maze has always been there; the strange pair of gates set in the side of a mountain a common feature in every painting of the area, no matter how ancient. One white, one red, nobody knows what they're made of but they resist any attempt to damage them; they’re always slightly cool to the touch no matter the weather, they have a very reflective surface, and if you look at them in a bright light, sometimes it looks as if they glow on their own.
The important thing is what’s on the other side of them, of course. The Maze itself is a strange place where the normal rules are suspended, and its own set takes their place. It’s a place filled with puzzles and riddles, monsters and traps; it’s always consistent with itself in any single run but is never the same two times around, and sometimes you could swear it has a sadistic streak, delighting in tricking the unwary adventurer.
It is a dangerous place, as so many people will rush to tell you; most people who go in never come out, and even those who do usually end up scarred for life. They also bring out with them enormous piles of riches, which is why people keep going in anyway.