Serial Killer Shapeshifter

The Serial Killer Shapeshifter was a shapeshifter who acted as a serial killer.

Background
This shapeshifter would impersonate the loved ones of various people and then kill their significant other while looking for someone to love it. After the shapeshifter took on the form of Zach Warren and killed his girlfriend, Sam learned of the incident from Zach's sister Rebecca and insisted he and Dean check it out as he believed that Zach was innocent. After seeing a dog bark insistently, having been changed by the presence of the shapeshifter and its retinal flare on a security video, Sam and Dean realize they might be dealing with something supernatural and decide to investigate further. At the same time, the shapeshifter impersonates a man named Alex and attacks his wife, Lindsay, but is caught in the act as Alex comes home early. The shapeshifter knocks Alex out and flees, leaving it looking like it was Alex who attacked his wife. After hearing the man's story, Sam and Dean realize they are dealing with a shapeshifter, though they have never fought one of this type before. Investigating the sewers, Sam and Dean find the shapeshifter's lair and are attacked by it, but it runs off when they shoot at it. When Sam and Dean try to chase it down, the shapeshifter ambushes Dean, locks him in its lair and then takes his form to ambush Sam, however, Sam sees through its disguise. When Sam hesitates to shoot it, the shapeshifter knocks him out with a crowbar and locks him in its lair before going after Rebecca. Arriving at Rebecca's, it convinces her to let it in and tells her what's really doing the killings to get close to her. However, it starts to freak her out and when she tries to call the police, it attacks her and ties her up. However, before he can kill Rebecca, the police arrive due to Sam and Dean escaping and calling them and it is forced to run, injuring an officer on its way out and implicating Dean in its crimes. After escaping, the shapeshifter eventually returns and takes Rebecca captive, taking on her form and tying her up in its lair in the sewers where Dean finds and rescues her. At the same time, the shapeshifter pretends to be Rebecca and ambushes Sam, knocking him out and tying him up before retaking Dean's form. The shapeshifter reveals that it plans to frame Dean for the murder of Sam so he will be hunted for the rest of his life, but Sam breaks free and fights it. Sam is no match for the shapeshifter and it starts to strangle him to death, but Dean arrives and shoots the shapeshifter twice in the heart with silver bullets, killing it. As the shapeshifter was caught in the act of trying to kill Rebecca in Dean's form, Dean is blamed and Zach and Alex are released. The shapeshifter is buried in Dean's form and under his name, allowing him to fake his death.

Powers and Abilities

 * Shapeshifting - As a shapeshifter, it could change its form into the forms of the living and the dead. As long as the person it was impersonating was alive, it could access their thoughts and memories to help with its disguise.
 * Superhuman strength - The shapeshifter was easily stronger than Sam when they fought each other.
 * Superhuman speed - The shapeshifter was extremely fast, able to run faster than a gun could be aimed and escape multiple times.
 * Superhuman agility - The shapeshifter was able to dodge a bullet, jump out of a house without hurting itself, and left a bloody footprint on a telephone pole, indicating it was able to climb it.
 * Regeneration - Shapeshifters can heal non-fatal wounds and even replace body parts by changing form.

Weaknesses

 * Silver - Dean killed the shapeshifter with silver bullets.
 * Retinal Flare - The shapeshifter could be identified by its retinal flare on cameras.
 * Dogs - Part of the reason Sam and Dean realized they were dealing with a supernatural creature was a friendly dog became vicious after the shapeshifter killed one of its neighbors.

Appearances

 * Season 1
 * Skin

Trivia

 * This is the first shapeshifter that Sam and Dean have ever encountered in their lives given their comments while fighting it.