The night before St. Nicholas
Krampusnacht is the night of December 5, the eve of the Feast of St. Nicholas on December 6. In Alpine tradition, St. Nicholas rewards the well-behaved children, and Krampus punishes the badly behaved ones with birch rods.
Source: Wikipedia, "Krampus"
Chains, bells and a basket
Krampus is usually shown with horns and fur, carrying chains, bells of various sizes, a bundle of birch branches, and a sack or basket on his back for taking the worst children away. The name is often traced to the German Krampen, "claw."
Sources: Wikipedia, Smithsonian
The Krampus run
In a Krampuslauf, or "Krampus run," people dressed as Krampus parade through town and scare the crowd. The tradition has been growing again since the late twentieth century, and North American Krampus events are growing with it.
Source: Wikipedia
Greetings from Krampus
Europeans have exchanged Krampus greeting cards, Krampuskarten, since the nineteenth century, usually with a humorous rhyme. Many of the old cards are now in the public domain.
Sources: Wikipedia, The Public Domain Review
Banned, and back
In 1930s Austria, the Dollfuss regime prohibited the Krampus tradition, and in the 1950s the Austrian government handed out pamphlets titled "Krampus Is an Evil Man." Neither stuck.
Source: Wikipedia
Frau Perchta
The co-hostess of our party comes from the same mountains. Perchta roams during the Rauhnächte, the twelve nights between Christmas and Epiphany, in two forms: a beautiful woman in white, or a crone. In parts of Austria and Bavaria, processions of "beautiful" and "ugly" Perchten still walk those nights.
Source: Atlas Obscura
You will read that Krampus is a pagan god thousands of years old. Some writers say so. Historians generally consider it unlikely, because he doesn't appear in the record until the sixteenth century. Tell it at the party anyway, and let the room decide.