- You may be looking for the starship Cerberus.
When Katarina and the First Doctor approached Cerberus, it would not let them pass. Charon explained that it would only let Katarina pass, as the Doctor was not dead. She refused to leave the Doctor. He fashioned a dog-whistle and contrived to have it whistle continuously. While the beast was distracted, they made their way past it. (PROSE: Katarina in the Underworld)
A Cerberus (with two fake heads) was one of the attractions at the Ancient Worlds theme park on Dewyn. It came under the control of a Chiffala and was used to attack guests attending the park. (COMIC: Minor Trouble / Inhuman Sacrifice / Crimes and Punishment)