Doppleganger

A doppleganger is a soulless negative creature located in the Never-realm. It takes on the form of whomever they choose, even gaining some of their abilities, and usually decides to kill those they copy in order to take on their lives an a feebled attempt to have something they are cursed to never have.

How to Find out if your partner has be stolen by a Doppleganger:

 * The Doppleganger can not talk as the person they are copying.
 * A Doppleganger tends to lean to the left after periods of long stress, its true form shifting into existence for a moment before returning back to their cloned form.