"it's a very unusual way of travelling"
Another prompt referencing the time travel in The Christmas Mystery. Honestly, I think these are the worst! It took me hours and lots of really stupid ideas until I came up with a - very imperfect - idea of an unusual way of travelling: through a kind of surveillance picture/portal in the guard's cave. If you don't like it, believe me, it could have been a lot worse.
So, who do you think those two are? I think it's pretty obvious, but then, I currently live with these characters in my head and know them better than you do (or at least I hope so).
By the way, I hope you had a wonderful Christmas!