A cyber-species exists and can travel and communicate across a worldwide network of some object or element, such as iron, igneous rock, or potatoes.
A race or species physically incapable of moving anywhere alone; they must move in a group, or their bodies cease to function until a group picks them up.
In a world where the only sentient race is seafaring, people (mers, or whatever your preferred sea species is) build landboats to cross continents. These landboats prove insufficient due to differing weather conditions, rough terrain, wild animals, etc. Your protagonist is one of the people trying to figure out how to overcome these conditions.
A world in which mastery of languages is the quickest way to gain influence, as nearly every country has its own language — and some languages even differ from kingdom to country.
A governor or king makes a law that music and poetry must be more honest. So instead of a face launching a thousand ships, the face could possibly make the ship move a little if shoved against it hard enough, beauty notwithstanding. Your protagonist is a poet who previously made a living off hyperbole, and now speaks his poems with other disgruntled artists in the poetic equivalent of the black market.
Once a year, people from all over the world take a day off of whatever wars are going on to play soccer with each other.
(I missed one. Two today.)
A parallel universe exists a year in the past of the current universe as a sort of backup in case anything happens to the current universe. Write about a time when something did happen to wipe out the first universe, and the sentient beings in the backup have to figure out what happened in the next year and solve the problem before it’s too late.
Luck is directly tied to piety. The more pious an individual is, the more likely they are to catch lucky breaks, be in the right place at the right time, and score one-in-a-million shots at whatever.
In battle, warriors use trading cards to battle each other with giant holographic dragons and monsters. No one actually knows how to fight hand-to-hand.
Two clans at war unknowingly hire the same assassin to help them win.