A protagonist who can only communicate through grunts and yells, in the vein of Link.
Three heroes try to impede each other’s quests to become strong enough to kill the evil overlord. Rather than intervene, the evil overlord lets them have at each other. They kill each other’s best friends, love interests, wise old mentors, older brothers, dogs, etc. until one hero stands, and as it turns out, his actions made the evil overlord look tame in comparison. The overlord congratulates him, hands over the crown of evil, and walks away.
Your hero is presented with a choice between becoming a good overlord, all ill intent obliterated from his mind, or an evil overlord with all good intent obliterated from his mind. While this may seem like an obvious choice, becoming an evil overlord also permanently removes every virus or illness (e.g. cancer, AIDS, malaria) from existence. On top of that, your hero’s grandma/little sister/wise old mentor/insert sympathetic figure here is terminally ill. What does he choose?
A social movement that forces heroes not to kill faceless soldiers if they’re not human (e.g. elves, goblins, etc.). As a result of this, evil overlords hire exclusively non-humans to capture and kill heroes.
Goblins, slimes, and sentient rats rise up against the young human heroes and heroines who keep killing them to “level up” enough to fight some vague threat that doesn’t concern the former parties.
Food and drink combinations that grant different types of magical power. Food alone or drink alone does nothing, but, say, almond milk combined with milk chocolate gives a huge strength boost.
A factory that mass-produces heroes and heroines for struggling villages to buy and use against their respective evil overlord types.
A world in which people gain experience points for every task they complete. These experience points build into a mostly arbitrary level system that determines what privileges they have within society, such as voting or reproduction.
A species of sentient creatures shaped like beds, that can also serve as beds. These bed-beasts can’t move on their own, and draw nutrients from the humans that sleep on them, while also providing nutrients that help humans sleep better and wake up faster.
Maybe toss in some disgruntled traditional bed-makers in there somewhere.
A world composed almost entirely of teenage high fantasy protagonists and their evil overlord foils (who may or may not be the protagonists’ fathers).