Doppelgänger

Doppelgängers, also known as Shadow-Selves or Mortal Shadow Selves, are a supernatural occurrence that were created by Nature.

Creation
The phenomenon of the shadow-self occurs to counterbalance a disruption to Nature's law that all living things must die.

Powers and Abilities

 * Blood: Doppelgängers, being mystical and recurrent, are massive sources of magical power.
 * The blood of a doppelgänger can be used to link supernatural beings with the help of magic conducted by any witch.
 * Their blood can also be used to bind an extremely powerful curse or spell or to use as a power source in spells that require more magic than the witch in question possesses on their own.
 * For some spells, the blood must come from a human doppelgänger. For other spells, the blood of a doppelgänger can still be used even if they've been turned into a vampire.
 * The blood of the last two "living" doppelgängers can be used to reverse spells cast using non-traditional forms of magic, especially Spirit Magic (e.g. turning a vampire back into a (dead) human, undoing the spell that bound the Other Side, reversing the spells cast on daylight rings for vampires, removing a triggered gene in those cursed with lycanthropy, etc).
 * Linking: Doppelgängers, being modeled after immortals and other doppelgängers, have an inherently strong mystical connection to each other that can be used to invoke linking spells.
 * Unique Physiology: Doppelgängers are fully capable of being turned into vampires, and can retain the mystical properties of their blood despite their vampiric abilities. Since they can also be born witches, it can be assumed that doppelgängers could theoretically also be born as other supernatural species, such werewolves or Brotherhood of the Five hunters.

Weaknesses

 * Magic: Doppelgängers are susceptible to the powers of witchcraft. This is inclusive of mystical objects such as Papa Tunde's Blade, and Dark Objects.
 * Mortality: Despite of their supernatural status, doppelgängers are very much human and share many of the same weaknesses as non-supernatural beings (e.g. age, decapitation, disease, heart-failure, suffocation, etc.)