In a campaign I ran a while back, I had a recurring "character" that was a bumbling animated burlap sack that liked to collect things it could fit inside itself. It was a possible random encounter in every environment and my party encountered it a few times.
Besides being animated, it's only other powers were being very hard to catch and constantly emanating this song somehow: https://m.youtube.com/watch?v=5f0J-za7Xy0
Dumb, I know, but it was funny. The players liked it and called it Sacky. They tried to keep it as a pet but it would always just wander off when they gave it the opportunity. If the players could catch the thing when they saw it, it would yield whatever random bullshit it had collected since last they saw it. Usually useless items like rotten apples and rocks. But they did once find a +1 dagger, as well as a human skull. Now all this was rolled off a list of random shit and wasn't supposed to have any meaning behind it. The players shrugged off the skull as maybe something it found in the woods or a dungeon.
Cut to next time they find the thing and catch it, I roll (and at the same time find out that the list contains) a small child.
So the party rescue some rando orphan kid the bag had apparently managed to catch and connected it with the skull to come to the conclusion that the bag somehow ate people. They burned it to cinders.
Thus ended the reign of terror of Sacky the animated burlap sack.