Happy looking fishlizard people, the Terileptil were divas. They loved making everything pretty and shiny, artful, and beautiful. When they weren’t doing that, they were trying to do bad guy stuff like dressing up androids to be the grim reaper to scare locals away from their base. They also want to destroy all the humans with a plague, which is distressing to the Doctor and his companions.

They save the day and accidentally cause the Great Fire of London at the same time. So they saved one day, and ruined another. But that is pretty  much how Doctor Who always goes.

They were seen in The Visitation