Replica

Replicas are creatures that appear in Sonic Forces. They are distinct, virtual reality projections of existing lifeforms, created by Infinite with the power of the Phantom Ruby. Serving the Eggman Empire, replicas have all the strengths and powers that their original counterparts possess, though they have no free will. Each replicate can also be mass-produced.

Anatomy
Replicas, as the name implies, are virtual reality projections of existing lifeforms. The replicas take on the form of their original counterparts, with little to no differences between comparing the original to the fake (the replica of Shadow is shown to have different eyes than the original Shadow, namely having slitted, cat-like pupils). It is also worth noting that the replicas will occasionally have red pixels randomly appearing on their body, a likely factor from the Phantom Ruby's abilities.

Powers and abilities
Replicas are capable to using any ability that their original counterpart can utilize. The replica of Zavok, for example, is capable of fighting against Sonic in a brawl with both the personality and strength that the original Zavok has.

Past
Using the power of the Phantom Ruby, Infinite was able to create virtual reality replicas of Rouge the Bat and E-123 Omega. In the Virtual Reality, the replica of Rouge talks to Shadow over the radio, stating that Omega disappeared at this facility three months ago. Shadow is confused about what happened to Infinite, but makes his way through the area regardless.

Later on, Shadow reaches the point where Omega was defeated, but cannot find any sign of him. Rouge calmly states that this is because it never really happened. At this point, the replica of Omega joins the radio, stating that he has never been defeated before breaking down into constantly shouting "I am not weak".

Sonic Forces
Infinite later created virtual reality projections of Shadow, Metal Sonic, Chaos and Zavok. In the City, Sonic had rescued Tails and several civilians from the clutches of Dr. Eggman, but was shortly subdued by Infinite and his gang of replicas.

Six months would pass before Sonic was freed from inside the Death Egg, to which he fought the replica of Zavok. After defeating Zavok, the replica disintegrated, with Sonic noticing the sound Zavok made when he vanished, the very same sound used when the Phantom Ruby was in use. However, he was not able to give the matter much thought, as Sonic was forced to escape quickly due to the prison cell area undergoing violent convulsions. Around the same time, the Chaos replica ambushed and attempted to kill Tails, although the timely arrival of Classic Sonic made short work of the copy. Sonic later returned to the City after the Shadow replica was spotted leading Eggman's army on a rampage through the desolate town. When Sonic confronted the replica, the real Shadow arrived and defeated his replica. After the fight, Shadow revealed to Sonic what replicas were, giving the Resistance some insight to Infinite's power. Eventually, Sonic and the Avatar proceeded to fight Metal Sonic's replica, which had grown in size.

Eventually, the Resistance would reach the Eggman Empire Fortress, where an army of replicas would serve during the climatic battle between the Eggman Empire and Resistance. The creation of replicas was further increased by the thousands after the generator was destroyed, due to Eggman using the generator as a decoy while powering the Death Egg Robot with the actual Phantom Ruby (which was overclocked). Once the Death Egg Robot was destroyed and the Phantom Ruby along with it, the replicas that fought against the Resistance vanished.

Trivia

 * Shadow and Chaos are the only two replicas that do not have their own boss fight in Sonic Forces.
 * After both Sonic and the Avatar defeated Infinite, an army of "Infinite replicas" were fighting against the Resistance.
 * However the replicas of Infinite were not seen during the cutscene.
 * Although Shadow and various other characters stated that the replicas lacked the heart and soul of the originals, it seems that they at the very least possessed the memories of the original, as Zavok when defeated by Sonic yells "No! How could I lose to the likes of you again?!", alluding to their previous encounter.
 * Zavok is the only replica that was seen speaking in the main game. In the Episode Shadow DLC, however, the Rouge and Omega replicas were seen speaking.