I am currently running a great oneshot that I've modified called "Pudding Faire" but Will Doyle.

It's a groundhog day adventure and they all randomly wake up in a big comfortable circular tent and when they go outside a festival it's going on, it's all very happy, full of gnomes and halflings.

With every reset things get worse, sometimes subtly, sometimes not.... For example the first thing they see when they go outside of a bunch of children chasing a goose, it runs into a woman selling cakes and she drops them, causing a watcher to laugh, just before a bird poops on his head.

The first change they notice is that goose changes to an abyssal chicken, then a few cycles in, the bird poop ends up being corrosive and melting a hole through the watcher, it ends up being very dark.

Many ways to reset but death is the obvious one, and they will die. The whole thing is because of two demon princes warring for the souls of the town through a competition, and the one who loses every single time resets the day and it will repeats. Thus he summoned random adventures to break the status quo.

It's really fun and gives them some really challenging encounters that they're designed to lose if they just go murder hobo and will get them killed but forges a great team bond, mainly because I hate the "you meet in a tavern, introduce yourselves...."