The trailer released as part of Children In Need teased the episode without actually revealing much at all. Basically how a teaser should work. In it it appears as though Santa Clause has crashed and its Clara with whom he interacts with first. The Doctor comes in later, though surely this must have happened after Santa knocked upon the Doctors door? It also indicates that the story will be magical, questioning why people stop believing in Santa. Because youre a fairytale, Clara responds to Santas question. I grew out of fairytales. This profound statement clearly reads as a response to Claras relationship with the Doctor himself. Who then turns up. He isnt at all surprised to see Clara, but she is surprised to see him. Next Santa takes a sinister turn as he tells the Doctor hes here to help. Help against what? Be sure to save some room for a tangerine, Doctor, Santa ends the teaser on, indicating that this middling Doctor is still very bad indeed