Non-mythos story by Joan Aiken published in Haunting Christmas Tales in 1991. The narrator is a headmaster for a school for delinquents who is relating a story of his childhood. Neglected by his parents and jealous of all the nice presents his sickly cousin gets, he finally crosses the line when she receives a pair of unusual dancing dolls that she names Crespian and Clairan, possibly taken from names on a map she had once seen. A prank to cover his theft of the dolls results in his cousin's demise and the eventual discovery of his possession of the dolls and their destruction due to the hypnotic pull they now exert over him.
The story has certain thematic similarities to the Yellow Mythos (especially the presence of curious dolls) and the dolls are mentioned in passing in The Yellow House and A Christmas In Carcosa by DJ Tyrer.