A known immortal traveling with the PCs kills an attacker, and is arrested and charged with murder, since immortals cannot kill in self defense, being immortal.
Held in a lead sheath the blade of this sword is tipped with uranium and any wound from it, even a tiny one, will go cancerous, although the effects may not show up for months or even years.
Along the sluggish Vanne River, the banks are lined with thick stands of tall bulrushes. These areas of wetland are considered ill-omened by the locals, for they hide the skeletal remains of thousands of grazing animals, washed downriver in a terrible flood decades before.
Adding to the uncanny reputation of the place is the occasional undead cow or goat that lurks there. The product of a necromancer's experiments some years before, these relatively harmless undead wander the area at night, startling livestock as they attempt to graze with them.
Jemas Lorne, the most celebrated poet of the age, was found dead, clutching a fragment of verse torn from his journal. The tantalizing fragment spoke of wealth:
Golden sands, empty and cold,
Treasure's crypt, forgotten gold.
Under stone, ancestor's doom,
Noble's prize, troubadour's tomb.
Rumours claim that the poet's father, an eccentric nobleman, had hidden much of his wealth before his death. Perhaps the missing journal has more clues?
Societies of beings who in some way reflect the dogmatic, superstitious, religious, idiotic, political, etc. views of large (or small) groups of people in real life.
The ancient prophet Oijas Bek uttered a cryptic prediction:
In the time of the Floating Ships,
In the Capitol of the Shattered Empire,
The False God will draw the people to his banner,
The Blasphemer shall don robes of righteousness.
No one is sure what he meant, but the various sects each have their theories, which they often fight over.
Thrown enchanted skulls make great necromantic 'grenades' releasing blasts of negative energy, incorporeal undead, swarms of flesh-eating worms, etc.
A land is reigned by a circle of powerful men who control every aspect of the citizen's life. This cabal changes members often. In reality, the spectres of a small necromantic covent possess and control the people in power. Since they simply possess the bodies, they can leave when old age overcomes their shells and possess a new up-and-coming noble.
A rich southern landowner once imported hundreds of thousands of spiders and distributed them along his long, tree-lined road. After a couple of days, when the spiders had make an incredible number of webs amongst the rows of trees, he spread fine gold and silver dust on them to create a spectacular shimmering view. (true story) It was for his daughter's wedding day.
There is a land where every person wears spectacles. Those without eyeglasses are considered to be the lowest stratum of society, so adventurers without glasses are treated like outcastes. It certainly would explain those heroes wearing sunglasses for no apparent reason...
The player characters, experienced and somewhat well known, hear rumors and travelers' tales about a distant area being overrun by dragons (or other terrifying monstrosities). The locals have sent them a message, begging for heroic aid.
When they investigate, they discover that nothing of the sort is going on. It turns out that a group of thieves wanted them out of the way so that they could rob them (or someone who would normally receive their protection).
The PCs encounter an elaborate trap room, designed to fill with water, drowning those inside. Clever and resourceful, they disable the trap and move on.
Only later do they discover that this room is part of the elaborate cooling system that prevents beasts of elemental fire from overrunning the complex. While the fiery beasts run rampant, they begin setting fires, which causes the complex to become increasingly hot and smoke-filled. Additionally, the PCs now have to fight their way out past aggressive fire creatures...
An alchemist enchanted his equipment to produce even more powerful alchemical compounds, potions and the like. Unfortunately, it is not well-known that he had different sets of equipment for different processes: If the wrong set of gear is used, the result will invariably fail to function. It's not a cursed item, just something that's hard to figure out.
In a city where the justice system features judicial dueling, plaintiffs and defendants are permitted to request a champion to take their place in the duel: Someone chosen by lot from among the foreigners in the city. When anyone first arrives, they are given an enchanted ceramic pendant that marks them as a candidate for "court duty".
Wealthy folk entering the city are often escorted by burly guards, paid to carry pendants on their behalf: They elude court duty in that way.
Adventurers may seek work as a rich man's proxy or may find themselves magically summoned to serve as a champion.
Certain trees have sap that is filled with magical potential. Their sap is harvested and distilled down to produce various types of potions, much like maple syrup is collected in some areas. The magical effects of these syrupy potions are often fairly trivial; perhaps they simply cause the imbiber to grow hair more quickly, summon butterflies, or walk a few inches above the floor. People enjoy the syrup as a flavoring, instead of imbibing it for its magical powers.
A powerful wizard that the PCs encounter is completely silent. He does not speak and cannot be heard as he moves. Even his spells are silent, but his magic is just as potent.
He has a tendency to summon invisible chairs, place foes in invisible boxes of force, and other "mime tricks".
A desolate region is almost entirely without normal vegetation. Local plants are able to unroot themselves and crawl along the ground in search of water and fertile soil. The inhabitants fence their crops in to keep them from wandering off and put heavy stone thresholds in the doorways of their huts to keep wayward plants out.
The plants sense by chemical cues, lacking sight or hearing, and tend to avoid herbivores or anything that smells of "dead plants". Characters with horses are likely to be unwelcome among the locals.
Giant mushrooms the size of trees. The stems and parts of the caps can be used in construction, and only the gills are soft enough to eat. An entire fungi-forest can grow in a matter of days, provided the correct conditions. Most fungus trees last about a month before collapsing, but not before a new generation sprouts to provide shade for the next spores.
Near a major city, a mirror image of the place has appeared. This strange double is infested with hostile insectoid humanoids that appear to match the city folk in numbers and armaments. The humans’ diviners have determined that the secret of the city’s appearance can be found within the double’s college of magic, so heroes are needed to explore within this mirror city and discover what has drawn it from its distant realm. There isn’t much time to spare, as the bug folk find their mammalian counterparts unnatural and blasphemous, and plan to destroy them.
This ring keeps soul in the body even when the wearer is killed, making bringing life back to the wearer much easier. However, if it takes too long, the wearer will begin to rot and become undead. Removing the ring causes the spirit to pass on immediately.
When you sleep, your soul briefly returns to the place where it was created/goes to when it dies, and seeks nourishment. Everybody's soul is created with a little link (or you could say a greater entity calls it back) to that place so that it can return easily, but upon death, the soul returns via that and annihilates the link as if returns.
Also, as an added thingy, you could say the entity supplying the link, or residue of the links themselves, (whichever) is the source of all arcane power.