White, bulbous monstrosities that appear to feed on the spirits of the departed. Originate from Moti, Plane of Death, first encountered in the abandoned town of Falandore outside the Forgotten Forest.

A giant floating ball with several dozen eyes emerges from the alley. It drifts over the city streets, casting a long shadow. Spirits scatter in fright. The creature's pale skin reveals bulging blue veins twisted into a tight ball at its center. White tentacles extend outward from its core. - Ghost-Eaters of the Forgotten Forest (RPA-ADV7) 

Ghost-Eaters are able to interact with beings in both the material world and the astral plane simultaneously;

The Ghost-Eater turns to you, wrapping its tentacles around your shoulders and neck. Then, with a sharp tug, your soul is ripped from your body. The Ghost-Eater feasts on your spectral form, and gradually your spirit begins to fade. - Ghost-Eaters of the Forgotten Forest (RPA-ADV7) 

The translucent appearance of the Ghost-Eater changes when feeding, almost as if the spirit it is draining pulses through its form;

The Ghost-Eater’s flesh, in contrast, begins to take on new life and vigor, its semi-transparent skin now flush with a rainbow of colors. - Ghost-Eaters of the Forgotten Forest (RPA-ADV7) 

Though Ghost-Eaters prefer to attack spirits, they can also prey on living beings by tearing their souls from their bodies. If the feeding is interrupted, their victims may find that the experience a form of astral projection with their spirits severed from their bodies. In some cases, the spirit can be reattached;

Then the Ghost-Eater’s thin tentacles float through the bars and wrap around the cat. The cat hisses at first but then stares blankly at its attacker as if paralyzed. A few moments later, the cat’s spirit is ripped from its body and is slowly absorbed into the Ghost-Eater. - Ghost-Eaters of the Forgotten Forest (RPA-ADV7)

Your spectral form escapes the Ghost-Eater’s grasp and floats upward, staring down at the Colosseum of Ashes from above.

It takes you quite some time to learn how to maneuver in your new form, but eventually you are able to fly through the arena. When you return to the black ash, you are able to lie down and merge your spirit with your body. - Tome of Encounters (RPA-SQ1)

Returning to life after having your spirit sucked from your body by a Ghost-Eater is an aging process;

Soon, you spot your own lifeless corpse by the river and find yourself falling back to the ground. When you land, you feel yourself sitting up and coughing violently. Your spirit has again merged with your physical form. You wake from your brush with death feeling older and somehow changed. - Backstory Codex - Doomed (RPA-BC)

Ghost-Eaters are capable of their own intelligent speech;

The disembodied head makes a strange gurgling noise. It’s hard to tell if it’s laughing or dry-heaving.

The Ghost-Eaters’ noises bear a striking resemblance to Gashto, the Demon tongue. - Ghost-Eaters of the Forgotten Forest (RPA-ADV7)

Ghost-Eaters are capable of using magic to “mark” others with a tattoo;

Before leaving, they mumble a few words over you and you feel your flesh tingling with magical energy. A strange tattoo, cast in golden ink, appears on your right arm.

The tattooed letters are written across your skin in golden ink, but you cannot decipher their meaning. You are uncertain of the purpose behind this gesture. Perhaps the markings are a protective spell. - Ghost-Eaters of the Forgotten Forest (RPA-ADV7)

Ghost-Eaters are first seen plaguing the ghosts that inhabit Falandore.

They also appear in other locations in and around the Forgotten Forest, including the Abandoned Watchtower and the Cemetery.

Zerith, a witch and member of the Starlit Door, attempted to study and tame the Ghost-Eaters near Falandore.

A Ghost-Eater is brought against you at the Colosseum of Ashes;

A giant floating head hovers over the black ash of the arena with many eyes and white tentacles that extend outward from its core and slither through the air like snakes. Its pale skin is semitransparent, revealing bulging blue veins twisted into a tight ball at its center. - Tome of Encounters (RPA-SQ1)

• Cut the Ghost-eater into ribbons and tally another win.
• Attempt to communicate with it:
  • Succeed, and it leaves of its own accord, curious about its conversation with you.
  • Fail, and you have no other option but to fight.
• The Ghost-Eater separates your spirit from your body and you observe the stands high above the arena before returning back to your body.

If you were marked by the Ghost-Eaters outside Falandore, this one at the Colosseum of Ashes will not fight you.

A Ghost-Eater joins the fight with Yuvan Rokta in Moti, Plane of Death, at the final battle of Brizoor Waal.

At the River Trail of the Forgotten Forest, you witness an Orc woman being attacked by a Ghost-Eater, while another heads in a different direction:

• Save the Orc, and go on a spiritual journey before being resurrected.
• Take on the giant Ghost-Eater, and go on a spiritual journey before returning to your body.