- You may be looking for the folkloric species.
This member of the Pantheon found its way into reality by a Time Field in Leadworth. He managed to fully enter reality by getting Veronica Stackmore, the spoiled daughter of the Mayor, to take his "gift for her". There he proceeded to send his servants to capture Amelia, Rory, and Mels. When they failed, he personally captured them and took them to the 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 come from. (COMIC: Imaginary Enemies)
Krampus's true form was revealed as a tall red being with a long tongue and ghastly features, but during his time attempting to erase Amelia, Rory, and Mels from existence, he remained disguised in a reverse Father Christmas suit with a long black beard. (COMIC: Imaginary Enemies)
The Pantheon member, whilst attempting to coax Veronica, seemed to be like Santa Claus — he appeared to be a kind man to Veronica telling her he was her uncle with a big smile. In truth, he despised the child and was only intending to use her to get rid of them, angrily telling her, "Just say ze vords [you] spoiled brat!" He hated returning to his point of existence as he screamed as he was dragged back into it. Krampus appeared to truly resent the young Amy and Rory as he angrily told them their own future, intentionally realising that he had told them the truth. The being, however, was flawed at explanations as he sometimes awkwardly laughed when Veronica knew he wasn't her actual uncle or when she heard him annoyed with her. (COMIC: Imaginary Enemies)