I liked the twist on this humanoid’s nature, though as a Welshman I’m disappointed I didn’t pick up on the rather obvious name. I think after the initial reveal thee menace disappeared a bit as the villain turned into just some snakes.
Colony Sarff was an agent of Davros and his head of personal security, performing tasks unsuitable to a standard Dalek. A colony of snakelike creatures, equipped with a nose, eyes and ears on separate snakes to form the illusion of a humanoid face. It is likely he was genetically engineered by Davros.