D&D One Shot

The PCs are an elite military squadron who must survive a rite of passage. A character is accompanied by an annoying sibling. It might involve spiders.
There is a religious will-o'-wisp who works against them. they are part of same organisation as a character.
The characters start with an explosion. Early on an ally turns out to be an enemy. If things slow down they uncover a secret stockpile.
It finishes with a reward of deeds to a village.

The PCs are blessed rogues who must negotiate with a celestial spider-drake. Two of the characters are friendly rivals. It might involve beholders.
There is a dangerous barbarian who works against them.
The characters start on the road about to encounter someone. Early on there is a romantic complication. If things are going nowhere someone discovers something unexpected in their pocket.
At the end there is a reward of an artifact.

The PCs are desperate humans who must destroy a cursed ruins in the Shadowfell. One or more characters has an inquisitive pet. The mood might be... action
There is a resourceful mercenary who wants to do the same thing. they share a passion with a character.
The characters start in a fight. At some point they encounter a symbol spell. If things get stuck someone hears a useful poem.
At the end there is the characters starting a journey.

The PCs are mercenary rogues who must escape from an elemental genie's home. One or more characters is currently is carrying a disease. It might involve water.
There is a mysterious paladin who hates one of the characters. they are the distant relation of a character.
The characters start with an escaped beast. At some point they encounter a magical door. If things get stuck one of their allies tries to leave.
Afterwards there is feasting in an inn.

The characters are all halflings that share a flying broomstick who must map out an elemental shrine. A character is accompanied by an annoying friend.
It is at an enchanted ruined keep which is near to a mordenkainen's magnificent mansion.
There are a mismatched group of intelligent animals injured in some way (not at full health). And a trustworthy watch captain seeks to explore a legendary planar fortress.
At some point a magic item develops new powers.
As the adventure progresses people start dying in different ways