Phantom (Final Fantasy)

The Phantom Ghosts are the souls of dead Phantoms. They are a hostile race, and attacked any living thing in sight. This also included the larger Phantom Ghosts that can be found in the wastelands such as in Tucson. Their bodies can go through any medium—like ghosts through a wall—and if this medium happened to be a living being, the Phantom Ghost will extract the being's soul and consume it.

History
Arriving on Earth on a large chunk of meteorite, the Phantom Ghosts invaded with little to no resistance. Phantom Ghosts come in many forms; though the invaders are mostly humanoid, there are also large insect-like and serpent-like Phantoms. The Phantom Ghosts are comprised of pure bio-etheric (spiritual) energy in a coherent form. Due to their unique properties, they drag the life-force and soul out of whatever organism they happen to touch. They can move through walls.

Curiosities

 * Phantom Ghost cells can infect bodies and souls.
 * Phantom Ghosts eat souls.
 * Phantom Ghosts can't be destroyed, just purificated.
 * A Phantom Ghost is invisible, but can turn himself visible with the radiation of a Barrier City.