Doomfinger

Mother Doomfinger was a Carrionite who, like the rest of her race, was banished to the Deep Darkness by the Eternals.

Doomfinger killed Peter when the Tenth Doctor, Martha Jones and Shakespeare visited him. She would have killed them as well, but the Doctor was able to name her as a Carrionite. By naming her, the Doctor banished her back to her kin. (DW: The Shakespeare Code)