Creature (Kill the Moon)

A creature lived in the Moon, a lunar body that orbited the planet Earth.

Biology
The creature was draconian in appearance, with four wings and a tail. Every hundred million years or so, the creature inside the Moon (which was really an egg) would hatch out and fly away into space. The creature would leave behind another egg or a "new Moon" that would continue to orbit Earth. (TV: Kill the Moon) It was described by Alice O'Donnell as a "big bat". (TV: Before the Flood)

History
In 2049, the current Moon began to show signs that it would break, which was the creature inside getting ready to be born. As the Moon began to crack open, bacteria from inside became a solid form and started to attack human astronauts who were on the Moon's surface. The only surviving astronaut, Lundvik made a plan to blow the Moon up to prevent the creature from being born and destroying Earth. However with help from Clara Oswald, Courtney Woods and in part the Twelfth Doctor they decided to instead let the creature be born. When it did, it flew away without harming Earth and left behind another egg. (TV: Kill the Moon)

Other realities
A version of Lundvik also existed, and went through similar events, in the Daft Dimension. However, after the creature laid the new egg, Clara Oswald questioned how the creature had laid an egg bigger than itself. In answer, the Doctor demonstrated that the "new moon" was extremely small but in closer orbit to compensate, snatching it out of the air. (COMIC: The Daft Dimension 480)