Greddels

Greddels are like mosquitoes, but with no thought or emotion. They have a penchant for ghosts and will tangle with their essence and suck them into the Final Death within a day. Always be vigilant in the field, because they attack without warning and mercy.
~Sage Mondigloe, to every Finder initiate class

Research:
Snake's Den Bestiary
by our sad Finder hero, Lorgan the Melancholy
In this Research Document:

What are Greddels

Greddels are the remaining essences of ghosts. Through happenstance, after a ghost succumbs to the Final Death, parts of their Ether form do not discorporate. This part has no thoughts, no feelings, only an insatiable thirst for energy.
If the Final Death is met at an official ritual site, the ghosts performing the rites take care of these sad remains before they become a problem. If the Final Death is met in the field and far away from a being able to discorporate them, and if the remaining essence discovers an energy source quickly enough, they can revitalize.
Their remaining existence is a constant hunt for energy.
New greddels look like nothing more than an evaporating late morning mist, their essence near discorporation. Once the essence gorges on power, it becomes larger and brighter. The more power absorbed, the more apparent they become. Old greddels look like ground-hugging clouds with static coursing over their exterior. Not much study has been done into what, exactly, the static is, but it's likely magic.
It makes a certain sense, that essences drained of energy want to absorb more, but the ghosts they once were a part of no longer exist. The wisps can't somehow return to that spiritual countenance. And as of this writing, there is no way to tell which ghostly essences might produce a greddel upon their Final Death. One might expect powerful whizens or mafiz, who overflow with magic, would create them, but it appears the more magical ability one has during their afterlife, the less likely they are to create a greddel.

Hidden Danger

Greddels, because they look like mist or fog, are often mistaken for these natural occurrences. Because mist is so ubiquitous in the Evenacht, a greddel can hide within it until it naturally dissipates, and if a being is nearby after they lose this energy-rich source, they will attack and attach to them.
Healers will cleanse population centers of any stray greddel, but Finders must be cautious when in the field. One never knows when a greddel has fused with a mist or cloud.

Greddels are singular entities; no spirit has created more than one upon Final Death.

While greddels can form anywhere, they are typically found in remote or inhospitable environments in the Evenacht, because those places are where ghosts who get into trouble are less likely to find help when they need it.
The Snake's Head Peninsula is renown for the number of greddels that traverse it--which is why I'm writing this for those who need to complete a Redemption there. Other places to watch for are:

• Gapp's Reign. Apparently volcanic activity = energy
• The poorly-inhabited Scorn creates them, and they drift south to richer energy pasteurs to Csdarling and Dulcet
• Same for Ambermint
• Voidlands and Sunderlands create many, sustain few because of how energy-deficient they are
• Remote areas of The Dark and the Parley Mountains have them because ghosts who get into trouble can't find help in time. Mist is more plentiful in these regions, so the greddels are larger and more deadly

Healing houses have special rooms for the removal of greddels. They contain apparatuses that will feed the vicitm energy, hoping to keep them in existence long enough to detangle the essences from one another. Once the ghost is freed, the healer places a shield about the greddel and leaves it in the room to fade into non-existence.
Greddels typically absorb the energy in the shield, then have no other source to sustain them. Five years usually elapses before healers believe it safe enough to reopen the room. The greddels are surely long-since discorporated into nothing, but there's no reason not to take extra precautions.

The Hunt for Energy

Greddels' soul purpose is to absorb energy. Because they begin with a lack of it, they hug the ground and slowly move. Once they sense energy, they follow it, and it's near impossible to evade them once they have discovered a power source. They will hunt whatever entity they sense, be that a native, an animal, mists, or a ghost.
The creatures attach their essence to their prey and begin to absorb. The living have an easier time getting away once a greddel latches onto them because their essence can't tangle with flesh. Once they shake off the cloud, running away is the only option, and if they don't escape fast enough, the greddel will reattach itself.
Because flesh is not as compatible with essence, greddels usually don't kill the natives they've attached to before those natives get help from a healer.
Ghosts, on the other hand, are in grave danger from these creatures. Not only is a greddel difficult to dislodge once it tangles is essence with a ghost's, it can drain the spirit into the final death within a day. An extremely powerful healer is needed to remove the greddel and remain whole, and, less ideal, a powerful whizen, mafiz or similar magic user.
Since the greddel wraps itself around the essence of its victim, and detangling it is terribly difficult. Once it sends its victim to the Final Death, it will go after the next available power source, which is the spirit helping the unlucky ghost.

Find the Greddel

Greddel 1 Reveal

Greddel 2 Reveal

Greddel 3 Reveal