Doppelganger

I’ve used a fantasy version of this in my stories.  For fantasy, these tend to be shapeshifters who copy a person and try to replace them.  At the very least, they take the form while occasionally copying all memories as well.  This makes it difficult for a person to notice the switch, which is why they are as dangerous as mimics.  None of that matters here because real-world doppelgangers aren’t that.

These are ghostly copies of living people right down to their mannerisms.  They aren’t always solid, but their features are clear.  Some stories have them speaking and interacting with their surroundings, which increases the confusion on them being the real person or the fake.  They are said to try to tempt and trick their targets into harmful actions either for their own entertainment or to replace them upon death.  This means they are dark and malevolent spirits that need to be avoided.

It’s that last part that has them listed as a death omen, which is similar to the banshee.  A key difference is that the doppelganger means the person viewing it will die and it might have a hand in the event.  Banshees typically only warn of a loved one dying soon and aren’t responsible.

An interesting aspect of doppelgangers are that they have no shadow or reflection.  This could be due to them not so much being a copy of a person, but a mirror-image.  They have no reflection because they are the reflection.  I couldn’t find much on this idea beyond a few suggestions.  Mostly it was that lack of a soul means it wouldn’t be shown in mirrors similar to a vampire.  The whole mirrors/glass are portals to the soul idea means such creatures wouldn’t register.

One has to wonder if they would really count as a ghost since they might lack a soul and don’t come from the deceased.  Yet, they are considered a death omen, which tends to be a ghostly role.