Not-thing

The Not-Things were creatures from beyond the universe that imitated the Fourteenth Doctor and Donna Noble when the TARDIS deposited them on a spaceship at the edge of creation.

Being capable of copying individuals completely, including their memories, the Not-Things were capable of copying Donna up to a 99.9% accurate level. They copied best at speed, working off of fear and the adrenaline response. They had trouble with shaping human arms and jaws specifically. (TV: )