Linking is a spell which allows a Witch to unite two or more elements as one, establishing a bond between the beings where the sensations and injury of one will also be inflicted on the other.
Linking spells can vary with the most extreme of cases, be used by a Coven to share power at the cost of also sharing their life-force such that linked beings who are can all potentially die if just one of the linked were to be killed in some way.
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 using the mystical properties of their blood.
Unlinking spells allows a witch to sever the magical link between two or more beings previously established by a linking spell.