Mim

The Mim were a race of purple sponges.

Biology
The Mim were mostly made up of nervous tissue. (BFBS: The Wake) They had purple, tentacled sponges and the ability to take on the shape of humans and Time Lords. (CC: Shadow of the Past)

History
One Mim came to the Earth in the early 1970s as an advance scout, while the rest of the fleet waited in orbit near the Earth. They wished to take over the Earth to use as a breeding planet. The Mim that landed on the Earth was locked in UNIT's Vault 75-73/Whitehall and started to take the form of Sergeant Robin Marshall. (CC: Shadow of the Past)

The Eighth Doctor and Lucie Miller once saved some Mim delegates on Northern New Mars. (ST: The Great Escapes)

The Mim fought a war with the Draconians at the start of the 27th century. (BFBS: Nobody's Children)