I need an object, plant, substance or word that is thought to stop a shapechanging creature/thing changing shape. It does need to be from folklore not a book or RPG.
I've searched on variations of - Stop, Shapechange, Shape, Change, Polymorph, Werewolf, Lycanthrope, Golem and Transubstantiation. All with no luck.
It doesn't need to apply to werewolves, or even something biological. It could be alchemical and would suit my purposes fine. It can also be from any folklore or myth from anywhere.
Any help much appreciated.
*****EDIT**** Got what I need now. Thank you all.