The Slitheen

From the planet Raxacricofallapatorius the Slitheen fammily are always into crimes. They were sentenced to death by their own species and they have a punishment for their crimes. They escaped from their planet and if they come back they will be boiled into soup. Female Raxacricofallapatorians can shoot a poison dart from their their claws.

to camouflage themselves they rip out the skin of people and use it as desguises. You may think they are big to fit in people's bodies but they have a rectracable machine in their necks to fit in there.