They're one of the many ghasts that can induce a depression. A L. starts out as a small creature, trying to enfold a body part. Usually it goes for the head. Every covered body part becomes numb, even pain is drowned out. A L. is easily sensed: Their presence induces a lack of energy, happiness and highlights misfortune. The more mature L.s wait until they grow strong enough to engulf their prey completely. They seem to be invisible to most humans.
How to fight it
I suggest blunt objects: fighting hammers, clubs, if you do not mind hurting the victim. The victims do not see a point in fighting. Gloomy thoughts are especially attractive to a L. So - prevent an attack by not allowing the Gloom to become more important than the Ungloom!gab