Time zombie

-->Time zombies were creatures once seemed to roam through the TARDIS.

They were in fact projections from the near future of the Eleventh Doctor, Clara Oswald, and Gregor & Tricky van Baalen, who had suffered seemingly fatal exposure to the TARDIS' Eye of Harmony. When realising that their future could be rewritten, the Doctor escaped the eye with Clara before they were transformed. He later sent back the message "Big Friendly Button" to a past version of himself, which prevented them all from being exposed to the eye in the first place, and thus no-one was ever transformed. (TV: Journey to the Centre of the TARDIS)

Behind the Scenes
Although Clara describes them as "zombies", the term "Time Zombie" is actually taken from the episode's end credits.