Shlitzen

Shlitzen was a bogeyman encountered in Feet of Clay when he tried to detain Angua and Cheery Littlebottom in the Undead bar Biers. She flipped a fluffy blanket over his head, causing him extreme existential uncertainty - he didn't know whether or not he existed. It is well known that children hide their heads under the blanket to escape from fear, so to hide the fear's head under a blanket is a very effective way of causing it to stop being frightening.