The Smashed Statue Garden
An art collector hires the PCs to investigate vandalism. Every couple of years for the past few decades, someone has broken into his statue garden and smashed one of the statues. Nothing is stolen, and nothing else is touched. All the smashed statues are from the same artist. It eventually turns out the the artist in question is a spellcaster and destroyed statues are actually people who have been turned to stone. The person who has been smashing them is a Marut inevitable (that's the life and death one) who has been destroying those whose alloted lifespans have run out
Fantasy Borg Cube
(spelljammer) In the middle of the pholgiston the characters come across an incongruous cube-shaped iron fortress filled with spawn-creating zombies controlled by an evil witch whose living head is grafted onto a zombie body
More Fun With Maruts
A cattle drive has been running late and now something is killing the cattle. It's a Marut inevitable who's come because the cattle are late to the slaughterhouse.
More Fun With Cattle
A Sibriex demon (that's the graft creating one) has passed through a ranch, and now all the steer have been converted back into very angry bulls with supernatural strength and barbarian-style rage abilities
The Underworld
The criminal underworld has teamed up with the actual underworld and now there's a bunch of mobster monsters with satanic powers running around.
Doctor Juvenile
(for a superhero RPG) A supervillain named Dr.Juvenile is threatening the city. His specialty is childish pranks writ large. The heroes need to stop him before he replaces all the oxygen tanks in the hospital with bottled farts and blows up the sewage treatment plant with a dumptruck full of fireworks
There's No Such Thing As A Rare Book
A Call of Cthulhu game set in modern times in which paranormal mythos activity has skyrocketed due to the fact that the Necronomicon, Pnakotic Fragments, Book of Eibon, Revelations of Glakii, etc are now freely available on the Miskatonic University website (and those of similar institutes of higher learning) to anybody who is interested.
Disorder In The Court
While in the Abyss the PCs are randomly abducted and taken to the courtroom layer of Woeful Escarand to stand trial for made-up charges. The "trial" starts out as a disorderly courtroom trial in which whichever side insults the other worst seems to have advantage (use bluff checks as per Dragonlance taunting rules) but after a short while, if the PCs are winning, it is changed to a trial by ordeal, consisting of aomething similar to a Double Dare obstacle course but much bigger and with demons taking potshots at the PCs, deadly booby traps, and offal and excrement instead of non-toxic fun slime, if they succeed at this the format is again changed, this time to trial by combat against the prosecutor, who is at least as surprised by this latest change as the PCs are and is not entirely prepared. If they kill the prosecutor they are allowed to go free.
The Replica
A magic item (possibly a sword or something) which was a family heirloom of a local noble has been missing for an undetermined period of time. Beyond it's base magical abilities It had been enchanted to not show up on detect magic to reduce incidents of people trying to steal it, but this also meant that when it was stolen - and replaced with a fake - the fake took some time to be noticed. Anyway the PCs need to track down the sword (or whatever)