Here's the summary from Wikipedia:
Krampus is a mythical creature who accompanies Saint Nicholas in various regions of the world during the Christmas season. Krampus acts in conjunction with Saint Nicholas; the latter gives gifts to good children, while the Krampus gives warnings and punishments to the bad children. Traditionally, young men dress up as the Krampus in the first two weeks of December... and roam the streets frightening children and women with rusty chains and bells. In some rural areas the tradition also includes birching by Krampus, especially of young females.There is a discussion thread at Reddit which includes some personal reminiscences, such as these:
Re the last comment, see the video below:Think about this: nowadays those guys need to be registered and carry a number (at least where I live), so you can identify them if they commit any crimes. That's because before people were robbed, beaten up, etc. by drunk and mask-wearing "Perchten" (that's another name for them) who used their anonymity to either just run amok or straighten out some grudge or two.
Being half-Austrian, I can vouch that Krampus is taken very seriously. Each year, he'd bring me a lump of coal and a sound hiding. I was pretty pragmatic about this, and felt that the extra coal would help the family warm, and I probably deserved the hiding.
When I was younger, my dad... took me and my younger sister to the local Hungarian club (living in Denmark)...where at some point the Krampus would appear, and when I was younger I was scared shitless by him, but luckily St. Nicholas would arrive and scare him away, and hand out chocolate and candy to the children. Later in the evening when we got home, we'd clean our boots, and put them in the window, and then at night St. Nicholas would come with candy, if we had been good children, or if we had been bad, he'd give us potatoes and onions. I remember my mom once got that.
Japan has a kind of anti-Santa too. The Namahage goes house to house in groups looking for naughty children to take away. The parents appease them by serving food and sake and assuring them that no bad children live there. The young guys that dress up as the Namahage tend to get a little drunk towards the end of their run. I saw one sling a 3-year-old boy over his shoulder and try to walk off, with the boy's mother half-heartedly chasing after. The kid was bawling in sheer terror while all the adults just laughed. "It's okay," someone assured us, "That namahage is his father".
Photo credits top, middle, bottom