Ace (Dalek duplicate), in keeping with precedent.
Talk about it here.
A duplicate of Ace was made by the Daleks to infiltrate the library on Kar-Charrat in the 42nd century. It was sent into the library, where it shut down the defences for the Daleks to enter. Because the Kar-Charratans could invade the Daleks casing, they sent it out to find the Doctor in the rainforest. It broke Cataloguer Prink's neck, but he managed to destroy it. (AUDIO: The Genocide Machine)