10 Doctor Who Easter Eggs Hidden In Plain Sight

In Twice Upon A Time, the Twelfth Doctor is undergoing his latest regeneration, though he tries stubbornly to resist it. Fed up with living too long, changing every so often and becoming an entirely new person, he doesn't want to go through with it. This is a feeling that's shared by the First Doctor and because of this, the TARDIS brings him into contact with his former self.

The Testimony, initially a seeming villain, present the Doctor(s) with a list of the names that they will come to be known as, which effectively becomes a rundown of different moments in the franchise. The Imp of the Pandorica, from the Eleventh Doctor's tenure, the destroyer of Skaro, from almost any Doctor's time. There is also reference to the Butcher of Skull Moon, which could relate to either the Eighth Doctor or the War Doctor, as this took place during the Time War.

The Shadow of the Valeyard is the last name that the Testimony calls the Doctor by, which is a direct reference to the Sixth Doctor serial The Trial of a Time Lord. The Valeyard is said to be a darker amalgamation of all of the worst parts of the Doctor, somewhere between his twelfth and final regeneration. While that number has come and gone, the reference to it here may be a sign that it is still to come.