Ghosts

Ghosts and Spirits are a strange anomaly that have befuddled many researchers.

Possible explination
It is expected that Ghosts are caused when someone dies in such a way that causes a massive surge of energy, such as a lightning strike or some form of explosion.

The person's mental state imprints on the energy at the moment of death and reigns it into a copy of themselves.

Valuable parts
If something strikes a ghost, that item absorbs a bit of their energy and has the chance to gain some property of the ghost's ability.