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 remain. Annihilation."

- Dr. Ventress' last words before being fully absorbed by the Shimmer. The Shimmer is the main antagonist of the science fiction horror mystery book Annihilation and its 2018 film adaptation. It is a mysterious extraterrestrial entity that arrives on Earth via meteorite and begins scrambling and combining the DNA of everything it touches.

History
The Shimmer arrived on Earth via meteorite, crashing into a lighthouse next to a park. The Shimmer began projecting an electromagnetic field around the lighthouse, mutating the plants and animals by mixing their DNA with that of others.

The Shimmer's field soon grew to encapsulate the entire park. The US Government soon took notice of the forcefield and, designating the area surrounded by the electromagentic field as "Area X", began sending squads of soldiers in to investigate, including one team that included Lena's husband Kane. In the movie, none of these teams return, though in the book, several squads that patrolled only the outer areas of Area X manage to report back and establish the "rules" of the Shimmer.

Eventually an all female team comprised of Lena, Dr. Ventress, Anya Thorensen, Josie Radek and Cass Shepherd was sent in to travel to the lighthouse and report back what they found. In the course of their journey there, the team was whittled down until only Lena and Ventress remained (Anya and Cass were both killed by a mutated bear, while Josie chose to allow herself to be absorbed and transformed into a plant by the Shimmer). After being separated from Dr. Ventress, Lena reaches the lighthouse, where she finds a hole in the bottom part of its wall and a video camera on a tripod set up next to a dead, disintegrated body sitting beside the wall. Looking at the last thing recorded on the video camera, Lena discovers a video of Kane where he declares that he no longer knows if he still is himself due to the Shimmer scrambling his DNA, revealing that his flesh now moves similar to a liquid. He then ignites a phosphorous grenade and blows himself up before another Kane walks onscreen and turns off the camera.

Shocked by her discovery, Lena ultimately decides to venture down into the hole where she finds a vast, empty chamber and Dr. Ventress, who had now been partially absorbed into the Shimmer and had her DNA war[ed with and her eyes apparently removed. Ventress announces to Lena that the Shimmer will continue to absorb everything and fragment its genetic structure until it has been obliterated, before being fully assimilated into the Shimmer. The Shimmer then reveals itself to Lena, taking the form of a shapeless, glowing, seemingly cloudy fractal. It intakes a drop of blood from Lena and uses it to create a humanoid entity that mimics Lena. Lena first tries shooting the humanoid, only for her bullets to be absorbed by the entity. She then dashes out of the chamber and back up to the lighthouse, where she finds the humanoid entity waiting for her.

Lena then tries to attack it with brute force, only for the entity to mimic her attack and knock her back. She attempts to run out the lighthouse door, but the entity also runs towards it and pins her up against it, preventing her from opening. However, upon realizing that the entity would mimic everything she did, Lena gives the humanoid a phosphorous grenade and causes it to inherit her suicidal urges before causing it to activate the grenade and set itself aflame. As Lena runs out of and away from the lighthouse, the entity stumbles around the lighthouse, causing the area around it to burn before finding itself back down the hole and in the underground chamber, which it sets on fire as well. The fire spreads across all of the entity's creations, causing them to burn and disintegrating the force-field around the park.

Personality
The Shimmer is a being without an apparent will, existing only to propagate itself across the universe and assimilate everything into it. In addition to being able mix DNA and mutate things, the Shimmer is also capable of creating near perfect clones of sapient beings that inherit all of the original's DNA, personality and memories.

Trivia

 * The Shimmer is similar to the Thing, being an entity capable of copying and impersonating the DNA of any being it comes into contact with.
 * The Shimmer is also similar to the Flood from the Halo franchise, as they both appear to share the goal of assimilating every living being into themselves.