Mim

The Mim were a race of purple sponges.

The Mim were given lists of human words and often chose names closely relating to sponges in order to come off as humerous and non-threatening to outsiders. (PROSE: All Mimsy Were the Borogroves)

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

Evolution
Half a billion years before the 27th century the native sponges on the Mimsphere were developing eyes, stingers, anything that would give them an advantage in the fight for food. Soon after they learned they could eat each other. When that happened they found they could make themselves look like rocks to avoid being eaten. Thus their shapeshifting abilities were discovered. (PROSE: All Mimsy Were the Borogroves)

According to the "Joyce-Gate hypothesis," the Mim were actually slime molds possessed by intelligences from higher dimensions. (PROSE: All Mimsy Were the Borogroves)

Early interactions with humanity
The Mim were responsible for the destruction of the Library of Alexandria in the 5th century. (AUDIO: The Library of Alexandria)

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. (AUDIO: Shadow of the Past)

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

War with the Draconians
The Mim fought a war with the Draconians at the start of the 27th century. (PROSE: All Mimsy Were the Borogroves)

Irving Braxiatel saw the Mim were seen as a credible threat to the Braxiatel Collection. (PROSE: Parallel Lives) After Braxiatel left the Collection, Parasiel considered the Mim to be one of the most major threats to the place. (AUDIO: The Crystal of Cantus)

During the war against the Draconian Empire, Draconian ambassador Kothar revealed that he intended to get the courts to argue that the Mim were non-sentient, thus allowing the Draconians to use a slew of new weapons otherwise prohibited by law. (AUDIO: The Judas Gift)

Their home planet, the Mimsphere, was destroyed by Hass. After being manipulated into it by Irving Braxiatel, he used the built up radiation stored in his pressure suit to destroy the planet. (AUDIO: Freedom of Information)

Later history
At some point after the 30th century, the Mim invaded New Houston. The First Doctor and Dodo helped a band of resistance fighters to repel the invaders. (AUDIO: The Yes Men)

In the 40th century, Martha Jones was offered the option of having water served in an immature Mim. (PROSE: The Pirate Loop)

According to the Sixth Doctor, through the Gogglebox one could see mankind's first interaction with the "mysterious" Mim. (AUDIO: The Reaping)