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 Phantoms—those resembling beasts—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 will extract the being's soul and consume it.

Curiosities
Phantom Ghost cells can infect body 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.