Stuffed animals, wooden practice dummies, scarecrows, rocking horses, wooden dummies, unattended suits of armor, mannequins, anything made to look creature like comes alive once it comes within a few miles of the town.
They don't feel pain, they don't tire, they don't make any noise even, they just keep coming towards the PCs (if they have any statues or figures or something in their inventory, it comes alive too.)
I'd say set it up so that they come across 1 or 2 of them and have them fight, make it a kind of tough fight so that they know that just a few are a challenge. Then after they finally manage to destroy them completely they hear some shuffling leaves or something coming from just beyond their vision, and there are 2 more of them, and then they hear a broken twig off to another side and 3 emerge, etc etc, the PCs are surrounded.
They run, and find a shack or an abandoned Inn place to hide and find a pool of blood, a little investigation and out back by a large pile of straw there's a pile of guts and blood and a large sewing needle with some bloody leather thread still attached.
Then they see a family come around the corner, the PCs can see that they have leather thread sewn all over their body, and one of them has a stitch missing and theres some straw poking out. Probably good to have a NPC redshirt who gets taken at some point only to come back and has a dead expression and is after the PCs.
As they escape or whatever they see some of the trees have been recently chopped down and there are piles of sawdust and some sculpting tools, and the fire at the blacksmith is going and they can hear a hammer clanking onto metal, etc, something or someone is carving, sewing, and forging more of them.
They should probably also be working on something, building a huge metal and bone and wood and skin monstrosity of some sort, and it looks like its getting kinda close to being done. They all just toil away in total silence except the sounds of axes chopping wood, metal being forged, except occasionally the PCs think they can hear a voice (insert either creepy little girl/roving mini-boss/whatever)