Doppelgangers

Not much is known about these creatures, but it's universally agreed that a doppelganger is a creature of evil.

One will take on the aspects of a person it was created to copy, though it will not be able to imitate the subject's personality until it has taken a physical piece of the original, commonly a strand of hair. Only then will it be a "true doppelganger."

The biggest danger when facing a doppelganger is that once they become "true doppelgangers," a link is formed with the original. Once the link is made, the doppelganger becomes, in essence, a part of the original, and killing it is very dangerous. If the doppelganger dies, it is similar to the original losing an organ: while survival is possible, it is not very likely.