Replicant Snatching

'After discussion in this forum discussion, this page is being merged into Kill and Replace, in that they are the same trope with two different names. Please add further examples to that page, not this page.' (October 2018)

So you're a plucky highly advanced cyborg, and you want to bring about the downfall of humanity through propagation of your own kind. Good for you!

Unfortunately, there's a problem. Because you're a physical being, you can't flat-out possess someone. Even if you can shape-shift into a perfect replica of a human, you can't just integrate yourself into normal human society, without any form of identity. Sooner or later you'll get the cops on your tail, and all they need to do is put you through a metal detector and it's Game Over. Even perfectly imitating a real individual will cause problems if the original shows up.

Then you see a Genre Blind Innocent Bystander mooking his way down an alley. Hmm.

The Innocent Bystander's family doesn't notice anything. Why should they? He's the same as he always was. As long as they don't check the one dumpster where you left his skinless corpse and his removed, scanned-for-memories brain, you're safe. In all your plucky advanced cyborg glory.

See also Dead Person Impersonation and You Are Who You Eat.

For media not listed here, see Kill and Replace.

Literature

 * In The War of the Dreaming, selkies refer to the skins as "jackets," and they can be made from any species' flesh. Weirdly enough, this is also played for comedy: high-ranking selkie switch skins so often the lower ranks are perpetually confused about their identities.
 * In John Dies at the End, Korrok's clones kill/replace the originals and proceed to go about their lives with all the memories of the original. For added authenticity, although the clones can be remote-controlled in emergencies, the replacements themselves lack alien memories and have no idea they're not the originals. This eventually leads
 * The premise of Impostor is that look-alike copies of key people can be sent after targets, exploding violently once contact is made. The hero is accused of being one such impostor.
 * Codex Alera's "watercrafting" can be used to imitate the appearances of others. This leads to a shock for one of our protagonists;
 * There is a reversal of this trope in Isaac Asimov's Evidence, where it is implied that a man who was crippled in an accident created a replicant for himself, who replaced him by his own consent,
 * Philip K. Dick's short story The Father-thing. When an alien takes the place of the protagonist's father, he eats his insides, leaving only a dry, dead skin behind.

Live-Action TV

 * Cromartie pulls a similar schtick in The Sarah Connor Chronicles; growing a new synthetic skin, undergoing plastic surgery to resemble an out-of-work actor, then killing him and assuming his identity.
 * Another terminator,  And
 * In The Sarah Connor Chronicles episode "Allison From Palmdale" it is revealed that Cameron is a machine doppelganger of  Later on, after being captured by the human resistance, Cameron suffers damage to her processor that results in

Tabletop Games

 * The Tsochar in the Lords of Madness supplement for Dungeons & Dragons are tentacle monsters that can insert themselves into a humanoid host and either tag along harmlessly or violently usurp the original person.
 * There are also doppelgangers, changelings, demonic and ghostly possession, several magic spells... Inventive players or DMs can find dozens of ways for a character or monster to replace someone or wear him like a puppet, with varying degrees of survivability for the victim.
 * Exalted has this as an ability of the Lunars; they can become another creature if they ritualistically stalk it for hours, kill it, then drink its heart's blood. They can do the same thing for humans, but they can only pick up the specific form of the human they killed. However, there are Knacks that allow them to shift the appearance of a form they've acquired, and, if they're feeling humane, Knacks that allow them to assume a form temporarily after partaking of a non-lethal amount of blood from their target, or take a human form permanently after knocking them out, or even sleeping with them.
 * This is the central concept of 44, in which the PCs are people who've had a close relative or friend replaced by a robot, and the GM controls the Section 44 conspiracy. Brilliantly, player characters can be replaced during the game, and join the GM on the bad guy side.
 * The roleplaying game Changeling: The Lost plays on this idea. The changelings of the title are actually the humans who were abducted (at any age, not just as babies) and taken away to Faerie; fetches, artificial beings crafted from random detritus and animated by The Fair Folk, take their place, and actually believe themselves to be the person they replaced. Getting your old life back may very well involve doing this, in reverse, to an innocent being who's totally unaware that it isn't really you.