• pcs were kidnapped/tricked into a dangerous place to be sacrificed/experimented on/turned into pie, they have four hours to escape before Elvis McEvil is finished preparing whatever.
• a long lost ruin/dungeon/secret lab has been discovered, because a metorite impact/a flood/an earthquake and Elvis McEvil is allready looting the place to obtain the blade of world ending/dna samples of a killer virus/an army of mutated chihuahuas
• townspeople keep disapearing, they are kidnapped by a cult/mad scientists/crazy bakers and are used by Elvis McEvil to further his evil plans.
• Every full moon an evil sorcerer/a cartel boss/a giant squirrel demands people to be sacrificed/lots of money/hazel nuts otherwise a portal to hell will be opened/the townhall will be bombed/the giant squirrel gets sad. the demands can not be met and tonight is full moon.
• there is cool shit in a secret hidden labyrinth underneath the cathedral.
• the evil under the cathedral/the university/the cemetery is about to escape, because whoever imprisoned it can’t complete the necessary ritual/keep a highly advanced sentintent computer system running/did not have enough hazel nuts to keep a giant squirrel happy which is now rampaging through the graveyard.the pcs must enable the keeper to do his job, do the job themselves.

One-shots work well with pretty much any cliché storyline that the players can swiftly get the grasp of and jump into without too much time spent on exposition or build-up.

“There is [Evil character] doing [evil stuff] in [place], please go and defeat them.”

The evil character could be a tyrant overtaxing the population, a ghost tormenting a small rural town, a lich in the nearby dungeon doing shady stuff, a dragon who kidnapped a princess, etc… Pretty much anything that the players may have familiarity with and without arguing too much about the best course of action.

Depending on the premise, you could lead the players straight to the dungeon, or let them investigate a bit and come up with a plan to infiltrate the evil character’s lair. Whatever you choose, keep it short and easy to do: one-shots have very little time to dwell on specific details or plot beats, and if your players waste too much time on the planning/investigation phase, there won’t be time left to actually fight the bad guy.

Even if it’s a one-shot that won’t ever have a follow-up, including loot for the players to find is always an exciting addition. Players, like crows, love shiny thingies :)

Some stuff like mysteries you need to be ready to tell the players they got it right, even if their idea is a little crazy. Players are famously bad at noticing details and remembering plot. But if you do some subtle shifting instead of going in with a fixed, canonical, right answer then it can be fun.

I did a one shot the other day that was about people being murdered. We found out they were being done in by golems, but the solution we came up with (do the golem creation ritual with the opposite elements) wasn’t what the GM had in mind. But they decided that our idea was good, so they went with it, and we all felt very smart.

I second the horror/scary movie trope suggestion. PCs being the hunted instead of the hunters means that the DM can keep the pacing tight and not getting derailed, as the enemy will find them wherever they go until they die or escape (or defeat the monster).

If you place them in a contained area where they have explore to find a way out, they can lay traps to slow down (or defeat) the monster, they can find clues as to the monsters strength or weakness, they can try to hide when they hear the monster drawing neat, they can find slightly helpful items (batteries that can be used for a flashlight or in a baby monitor as an early warning system, slippers for better sneaking but worse running, vodka for temporary HP but worse constitution, scissors or letter openers to distract in close combat for a chance to escape) but not straight up weapons, they can take damage to deal damage, or take damage to escape whenever they get found. The monster will let them think they’ve gotten away but they’ll never be safe, it will always find them while they’re in this location.

The goal can be survive until sunrise, or try to get as many people out of the haunted house as possible, or survive/beat a set amount of the attractions at a demons fair to be released. It’ll be lika a hit+run or cat+mouse game.

Stabber, think Scream with student partying a house during a snowstorm and suddenly one of them is killed.

There is something in the spaceship, think Alien also works better in one shot

Actually, most horror games work better in one shot because nobody believes in monsters and if you see one you want to run away, not hurt them

PC can progress/change during a one-shot. It’s often forgiven. You can go “20 years later…” In the middle of the game. That’s great