D&D One Shot

The PCs are imprisoned sages who must investigate the history of a beautiful pet. It might involve fiends.
There is a helpful alchemist who works against them.
The characters start on the road about to encounter someone. Early on foes try to ambush them. If things are going nowhere a character has to make a roll to notice something.
It finishes with a reward of membership of an elite group. Possible sequel... same adventure but everything larger

The PCs are troubled tieflings who must ransack an unusual demiplane. It might involve romance.
There is a well-dressed druid who tries to help them. they are the employer of a character.
The characters start with a fireball. At some point foes try to ambush them. If things are going nowhere someone tries to steal from them.
It finishes with a reward of a magical tower.

The PCs are rebel warlocks who must solve why they are stuck in a dream. A character is celebrating a birthday. It might involve water.
There is a religious druid who offers them aid.
The characters start camped and about to be attacked. Early on an ally turns out to be an enemy. If things are going nowhere there is a strong wind.
At the end there is a reward of a treasure map.

The characters are powerful undead hunters who must explore an isolated dragon's lair.
It is at a hidden wizard's tower which has stone statues in every corner.
There are a group of travellers performing a ritual. And a successful champion seeks to solve mystery of why they are still alive. They all remember dying but not all the details.
At some point they receive a useful sending.
As the adventure progresses people start breaking into song

The PCs are renowned instructors at an academy who must destroy a cult of devils. It might involve earth.
There is a shapechanging cleric who has important information for them.
The characters start on a sinking vessel. At some point there is a feast. If things get stuck they spot a lone enemy scout.
It finishes with a cut-scene of each character.