Slyther

Slythers are large, tentacled blob-like creatures native to Skaro.

History
During the 22nd century Dalek invasion of Earth, the Black Dalek used a Slyther to guard the Bedfordshire mines at night, where it killed and ate anything it found. After it attacked a small group of humans consisting of Ian Chesterton, Larry Madison, Wells, and Ashton (killing the latter), Ian hit it with a rock, causing it to fall down a pit to its death. (DW: The Dalek Invasion of Earth)

The Daleks used Slythers during their assault on Lan Beta. (NA: Parasite)

Parents alive during the Dalek invasion of Earth used stories of Slythers to scare their children into behaving over 30 years after the events of the invasion was stopped. (BFA: An Earthly Child)

A different looking Slyther is seen in the Graphic Novel The Only Good Dalek

Behind the Scenes

 * Terry Nation's original script called for the Slyther to be "like a huge black jelly fish" that would remain largely off-screen and never be seen in its entirety.
 * The Slyther costume was built by Shawcraft, the same company that built the Daleks. The studio's first version of the costume wasn't considered scary enough, so it was altered between episode 4 and 5.
 * The Slyther was operated by Nick Evans, who was also a Dalek operator for this story.