Changeling

Changelings were individuals controlled by the Graske that mimicked a lifeform and sent the real one to Griffoth. They looked almost exactly like the originals, but their eyes flashed a greeny-gold colour occasionally, hinting at their true disposition. Changelings appeared to behave in just the same way as the originals, so that hardly anybody suspected them. (WC: )

The Pantheon of Discord used Changelings. The Tenth Doctor told the Trickster that he fought his shadows and Changelings. (TV: The Wedding of Sarah Jane Smith)

Behind the scenes

 * The changelings originally appeared in Attack of the Graske.
 * The player could choose from two outcomes with his or her remote control while playing Attack of the Graske. They could return the originals the changelings replaced to their rightful place, or freeze the chamber containing the originals, stopping the Graske but leaving the changelings on Earth.