Krampusnacht is part of holiday folklore in many central and eastern European countries where the horned creature known as Krampus punishes bad children on the night of December 5th (the night before the Feast of St. Nicholas). In some stories, he slaps bad children with birch branches, and in other, more extreme iterations, he may abduct them via a sack on his back to eat them (or engage in other torturous activities).
In many cases, Krampus appears along with Saint Nicholas (who is dressed in bishop vestments) who rewards children who behaved well throughout the year.
In modern times, Krampusnacht has become a celebratory festival where Krampus appears in town squares and holiday markets for entertainment purposes, and Pittsburgh gets into the fun with its own Krampusnacht festivities, aptly named Krampus Fest, in Market Square!
Note: The following article is based on my visit to Krampusnacht in 2021 which may have had some variations in setup due to COVID protocols. We cannot guarantee this will be the same format in future years. Keep in mind that while Krampusnacht is officially on December 5th, the city sometimes changes the date if other events are going on at the same time (read: Steelers games).