The Shimmer

"It's inside me now...It's not like us. It's unlike us. I don't know what it wants...or if it wants, but it will grow...until it encompasses everything. Our bodies and our minds will be fragmented into their smallest parts until...not one part remains. Annihilation."

- Ventress speaks her last words as she reveals that the Shimmer will consume everything before he assimilates and kills her.

The Shimmer is an amorphous being of unknown origin that crash landed on Earth and began to terraform the surrounding area and create what is known as Area X, which itself has been called "The Shimmer".

Physical Appearance
What is believed to be the Shimmer’s true appearance is similar to that of the Mandelbulb, a type of 3D fractal. It is multi-colored, and emits a glow from its center. Upon absorbing a drop of Lena’s blood, it used her DNA to create a featureless humanoid doppelgänger composed of a colorful, possibly metallic material, which eventually came to look exactly like her.

History
Landing in the middle of a lighthouse off the coast of Florida after hitching a ride on an asteroid, the Shimmer began to create a constantly expanding bubble-like barrier where everything that entered it began to (in a metaphorical sense) become refracted like light in bizarre ways such as the DNA of various organisms inside beginning to alter. The area inside said barrier was titled "Area X" and as it began to expand overtime, civilisation began to deteriorate, with vegetation and fungi growing at an exponential rate and turning what used to be a small, quiet town into an alien forest of monstrous creatures that used to be normal animals. As Area X was studied by a secret organisation known as the Southern Reach, various expeditions were sent into Area X with all of them never returning except emotionally empty duplicates of the expedition members who mysteriously return to the homes of who they appear to be without any trace of how they got there.

It is unknown what intentions the Shimmer has for creating Area X or the empty duplicates (if any at all). Based on the Shimmer's encounter with the Biologist of the twelve documented expedition were the Shimmer begins to change using the DNA from her blood to take a humanoid appearance and begins to mimic her, as if it was studying her movements and actions. Over time the Shimmer began to take on the appearance of the Biologist as their encounter progressed (which inherently explained the doppelgängers). In the 2018 film "Annihilation" which was based on the first book in the Southern Reach Trilogy, the Shimmer was killed by the Biologist when she tricked it into killing itself with an incendiary grenade which led to Area X reverting back to its previous state. However, it is implied that the Shimmer survived through the doppelgängers that its powers have created.

Appearances
The Shimmer appeared in the novel Southern Reach and its film adaptation Annihilation. It is the main antagonist both times.