|“||The sale of the century. We reduce the Earth to molten slag, then sell it piece by piece. Radioactive chunks, capable of powering every cut-price star liner and budget cargo ship. There's a recession out there, Doctor. People are buying cheap. This rock becomes raw fuel||„|
|~ Blon revealing the Slitheen's plan to the Doctor|
Blon Fel-Fotch Passameer-Day Slitheen (also known as Margaret Blaine is a member of the Slitheen a family of alien criminals. She appears in the Doctor Who episodes Aliens of London and World War Three as a secondary antagonist and Boom Town as the main antagonist (making her the most recurring Slitheen in the franchise).
When she is Margaret Blaine she is portrayed by Annette Badland (who also voices her when she is in her true form) and was portrayed by Alan Ruscoe in her true form and also portrayed as Babe Smith in Eastenders'.
Not much is known about Blon's earlier life but it is revealed that she did not want to take part in her family's criminal activities but was made to carry out her first hunt when she was thirteen and knew that if she refused her father would have fed her to Vernom Grubs.
Aliens of London and World War Three
Blon along her brother Jocrassa and other members of the Passameer-Day branch of the family came to Earth and disguised themselves as members of parliament using skin suits made from the skins of the politicians. Using the skin of a member of MI5 named Margaret Blaine, Blon aided her family in their plan to start a nuclear war on Earth in order to devastate the planet and sell the remaining chunks as fuel. This plan failed when Mickey Smith on the Ninth Doctor's orders fired a missile towards the Slitheen's base at 10 Downing Street and blew it up killing the aliens inside.
It was later revealed that Blon (still in the body of Margaret Blaine) had survived this incident by teleporting away seconds before the missile struck, but this was a one person teleporting device so she was unable take the other Slitheen with her. She arrives in Cardiff where she is made Mayor and makes a plan to build a nuclear power plant called Blaidd Dwrg (Welsh for Bad Wolf) where she would cause an "accident" so near a space rift there that it would destroy Earth and would provide her extrapolator significant power that she would "surf" into space to find any surviving members of her family.
She would kill anyone who questioned her plans, but in a rare moment of kindness, she spared a pregnant journalist named Cathy Salt who reminded her of her own lost family. The Doctor and his companions Rose Tyler, Jack Harkness and Mickey Smith arrived to stop her. Jack confiscated her extrapolator and refueled the TARDIS quicker whilst the Doctor was uncertain what to do with Blon as she was sentenced to death on her home planet Raxacoricofallapatorius. Blon pleaded the Doctor for mercy and clemency but when the extrapolator began to open the rift through the TARDIS, Blon threatened Rose and made Jack place the extrapolator at her feet. When the extrapolator began to tear apart the TARDIS, it's heart opened and Blon looked into it and was changed back into an egg (possibly meaning that the heart saw that Blon did want to change and decided to give her a second change at life) which the Doctor and the others took to Raxacoricofallapatorius to give to another family.
- Blon is one of two members of her family to have thought to have died but only to be revealed to have survived by teleporting away from danger in a later episode. The second member being Korst Gogg Thek Lutiven-Day Slitheen from Doctor Who's spin-off The Sarah Jane Adventures.