Mimic

The Mimics are a race of aliens from the 2014 film Edge of Tomorrow, in which they serve as the main antagonists.

Origin
For 5 years, humanity has been at war with an alien species called Mimics. NATO militaries have federated to create the United Defense Forces (UDF), with defeats escalating as the war continues. As the Mimics tighten their grip on Continental Europe, the introduction of armed mechanized exoskeletons called Jackets allows the UDF to achieve a decisive victory at Verdun. Major William Cage, a UDF spokesman and officer in the United States military, is summoned to London to meet with General Brigham, commander of the UDF. The UDF, inspired by the victory at Verdun, intends to launch Operation Downfall, a multi-front invasion of Mimic-controlled Europe which will relieve pressure on Russian and Chinese forces in Eastern Europe. Brigham orders Cage to cover combat on the beaches of Northwestern France, to which Cage objects, stating that he is not a soldier. When Cage tries to blackmail the General, he is arrested and stripped of rank. Cage is sent to base at Heathrow Airport, where he is to deploy from the following morning.

The next morning, Cage is dropped in with the first wave. To his horror, the Mimics have anticipated the attack, and annihilate the invasion force. Cage manages to kill an unusually large Mimic, but dies and is doused with its blood. Cage wakes up the previous morning at Heathrow, and is debriefed in the same manner. Cage discovers he is stuck in a time loop, and that every time he dies, he "resets" to the day prior to the invasion. Cage tries to convince soldiers at the base that the invasion will fail, to no avail. Cage loops several times, trying to save as many soldiers as he can. In one such loop, he saves the life of Rita Vrataski, the "Angel of Verdun" (or "Full Metal Bitch" behind her back), who, seeing Cage's ability to anticipate events of the battle, tells him to find her when he "wakes up." Both of them are then killed by an exploding drop ship.

At the base, Cage finds Rita, and tells her that they know each other from the following day's invasion. Rita confides in Cage that she too possessed the ability to "reset", which allowed her to kill hundreds of Mimics at Verdun singlehandedly, earning herself celebrity status. Rita tells Cage that the Mimics are controlled by a singular consciousness called the "Omega", which has the ability to reset time. Cage killed an Alpha Mimic and was doused in its blood, thereby gaining the ability to reset time. Rita gained that ability the same way, and lost it after receiving a blood transfusion. She also tells Cage that as the Mimics try to locate his consciousness, he will experience visions of the location of the Omega. Rita trains Cage in combat, and with each subsequent loop, Cage increases in proficiency. Rita and Cage team up during the invasion, and after dozens of loops, are finally able to make their way inland. Cage, in the meantime, has grown attached to Rita, and is finding it harder to see her being killed. The tension reaches a head when Cage tries to stop Rita from continuing, knowing that at their current location, Rita will be killed regardless. Rita ignores him and is mortally wounded trying to lift off in a helicopter. Cage comforts her as she dies, before he too is killed by the Mimics.

During his next loop, Cage, knowing that the Omega is in the Bavarian Alps, goes to kill the Omega himself. When he arrives at the dam from his visions, he is ambushed by an Alpha, who tries to steal his reset ability by killing him through exsanguination. Cage manages to die by drowning, preserving his ability. During his next loop, Cage tells Rita that the visions are just a hoax to corner him and steal his ability. Rita takes Cage to see Dr. Carter, a former government scientist and expert in Mimic biology. Carter explains to Cage that during his time working at Whitehall, he constructed a prototype transponder device, which can theoretically ascertain the location of the Omega if injected into an Alpha or someone with the "reset" ability. General Brigham supervised the construction of the device but declared it rubbish and had Carter dismissed. Rita and Cage infiltrate the Ministry of Defence, and threaten to kill Brigham unless he gives them the transponder. After several failed loops, Brigham relents and gives them the transponder.

Fleeing Whitehall with soldiers in hot pursuit, Rita stabs Cage with the transponder, and he concludes that the Omega is located under the Louvre. Cage removes the transponder, but Rita crashes into an armored soldier, knocking them both unconscious. Cage awakens hooked up to an IV, and realizes that the transfusion has taken away his power. Rita breaks Cage out, and they decide to try and kill the Omega that same night. To do so, Cage convinces soldiers from his squad to join them, already knowing the intimate details of their lives from his loops. The team flies to Paris, but are attacked by Mimics and forced into a crash-landing. Rita and Cage are the only ones to make it beneath the Louvre, where they find themselves being hunted by an Alpha. Rita gives Cage a grenade belt to kill the Omega, then kisses him, telling him "I only wish I could get to know you." Rita distracts the Alpha while Cage dives down to kill the Omega. The Alpha kills Rita, then dives down after Cage. The Alpha kills him, but not before he primes the grenade belt, which falls on the Omega, killing it, thereby crippling the Mimics.

As the Omega disintegrates, Cage's body absorbs its blood. Cage wakes up en route to his meeting with Brigham, and he attends a press conference where Brigham announces that the Mimics have seemingly given up and that the UDF is poised to liberate Europe. Cage, never having been stripped of rank, visits the Heathrow base, and goes to see Rita. Rita asks him what he wants, having never met him, to which Cage smiles.

Betas: The betas are the most common mimics. They look like bundles of metal wires with orange mouths. They can fire flaming projectiles that spin, making their smoke trails look vaguely like strands of DNA. The betas can easily bore through the ground and make surprise attacks. Alphas: The alphas are bigger and stronger than the betas and have bluish mouths. I believe Dr. Carter said that the alphas were 1 in 4 million.

Omega:  The Omega is the central intelligence of the mimics. It can control time and reset the day, making the mimics the deadliest species known to humanity.