Have You Heard About The Beast is a unique-encounter generator for fantasy adventuring games. It's clever, and it's also system neutral, but statting the beasts it spits out will take longer in something like 5e than it would in something like Mausritter due to 5e's more intricate statblocks.
Gameplay-wise, you all play as folks gossiping in a tavern about a regional beast, one-upping each other's details until you have a fully realized monster. Then all those rumors turn out to be true, and the adventurers have to go fight it.
There are prompts to make sure the beast always has certain key elements (like a special ability and a treasure) so the important bits are never left out, and there are also some tables for random features/abilities/treasures/etc so that you can use this without needing to play it.
I took a spin through it and came up with a regular cow that lives in a muddy hole next to a stream where no fish swim, that ate farmer Johnson's bull and spat the bones in his face, that can change its size to fit through a keyhole, that has coins for eyes, and that sneaks into your dreams and drains your soul. So basically A Wizard, but it's A Cow.
Some of the table entries are silly and some are sinister, so there's a very real chance of starting to build something ominous on the random tables only to find out that it can outdance any bard in the land, but if you play with a group and ignore the tables, you won't have this problem.
Overall, I think this is a really solid way of generating encounters for one-shots and sidequests. Nothing on the tables seemed deeply scary or unsettling (although mileage can vary a lot for this,) and it creates custom monsters and their accompanying folklore on demand. For groups that play fantasy adventure games, I would strongly recommend this as an additional piece of the GM's toolkit.
-Page 8, special ability, 7, "as its you from the inside out" as it eats you