From publisher blurb:
Several winter traditions revolve around festivals of gift-giving, gratitude, and hope for the new year, where good deeds and kindness throughout the year are rewarded with treats and presents. However, the children of the northern mountains also recognize the shorter days as a herald to the grim inquisition of Krampus. A reclusive devil exiled to the material plane, Krampus takes a particularly cruel delight in meting out justice to those who would think themselves above mortal law.
Building off of the existing Fifth Edition rules to build a warlock character, Krampus grants warlocks sinister powers to punish wrongdoers, all while tempting them to go too far in the name of revenge so that they, in turn, are punished by Krampus's other warlocks. This PDF also includes three additional eldritch invocations to further cement the holiday flavor of Christmas warlock option.