Pantheon of Discord

The Pantheon of Discord was a group of transcendental beings that sought to alter reality and cause chaos. The Trickster was an embodiment of one or more members of the Pantheon. The Doctor had heard legends of the Pantheon when he was a child and claimed to have fought the shadows and the changelings of the Pantheon in the past. (TV: The Wedding of Sarah Jane Smith)

History
Krampus, a member of the Pantheon, found its way into reality by a Time Field in Leadworth. He managed to fully enter reality by getting Veronica, the spoiled daughter of the Mayor, to take his "gift for her". There he proceeded to send his servants to capture Amy, Rory and Mels-when they failed, he personally captured them and took them to the school library. In order for him to fully have power he needed Veronica's wish, when at first she didn't want to he persuaded her to do so by showing her an image of Amy's Petrichor brand. However his plan was foiled when Amy told Veronica that her hands were dirty, and what she thought was her doll was in reality a lump of coal used to coax Veronica to bring him to Leadworth. She threw it back into the mirror as Krampus and his goons were forcibly dragged back into where they had originally came from, presumably for good. (COMIC: Imaginary Enemies)