Do impossible heroes really exist? Well, the Doctor certainly does, so why shouldn't Santa Claus? That was another question raised in Last Christmas and it's a concept which was perhaps more predominant with Robin Hood in Series 8's Robot of Sherwood. Whether you buy into it or not, It certainly looks like it's a theme the series will continue to explore for the foreseeable, anyway, and it's definitely an intriguing one because it pretty much brings anyone and everyone into the mix as far as the Doctor's future encounters are concerned. Will he be joining forces with Harry Potter in Series 9? Maybe an adventure with Luke Skywalker is on the cards? Perhaps that would be taking the idea a little too far. They're probably just laying the groundwork for that Doctor Who/Sherlock crossover that everyone keeps talking about...