Galla: These demons were never alive. Not in the same way as mortals that is to say. They have no concept of mercy, and cannot be bribed. They do have a concept of justice however. Their goal seems to be to get as many dead for the underworld as they can by whatever means they can.
This form of demon may not have a concept of mercy, but they do know the meaning of justice. Their duty is to maintain the laws of the underworld by whatever means they can. It is their duty to prevent physical escapes from the underworld, to maintain the laws protecting the rights of the dead in the underworld, and carry out the will of Ereshkigal.
They were dangerous, and occasionally rebellious. In a way they were something like bounty hunters. Even so, they were one of a few types of demon that were welcome to eat at the table of Enlil. (God of rain, wind and air)
Mashkimu: Underworld inspector.
Like the Galla, Maskim were underworld demons. Like the Galla, they were integral in the upkeep of the laws of the underworld. Unlike the Galla, they were tied more closely to the laws of the underworld than to the underworld itself.
Unlike many other vampiric creatures, the Maskim do not need to resort to sneaking up on their prey. Maskim can simply rip down the walls of a house and consume all that they find inside. They are demons of a much higher order than their underworld kinsmen.
Gidim: Encroaching darkness, hungry ghost.
Their name can be translated to encroaching darkness, hungry ghost, demon, or a hand full of other similar titles. The specifics are different, but the general points are the same. These are spirits who have the ability to consume the living in some way.
Not all dead who return to drink the blood of the living do so as a physical being. Gidim are walking shadows that consume the living leaving bruising upon the neck. They can possess a mortal by entering the ear, and so powerful charms are occasionally placed upon earrings to protect against them.
Gidim are ghostly demons who are often prevented from entering the land of the dead for one reason or another. This might be simply because they cannot offer gifts to each of the gate keepers, or be something far worse such as a profound hatred of some or all of the living. The journey back to the land of the living is difficult, but it can be done by a determined spirit, or on certain sacred days.
Not all Gidim are hostile towards the living. In the month of Ne Izi Gar ghosts return to the land of the living to visit their departed loved ones. They are welcomed with a number of festivals at this time. Also at this time the Gidim of hostile sorcerers are said to return. These ghosts can take the living and cause them several kinds of harm.
Two things seem to separate good Gidim from harmful ones. The harmful ones drink blood, and stay around longer. This makes sense when you consider that the dead need blood, the essence of life, to retain a link to the world of the living.
A final thing that should be remembered when looking at the Gidim are the sorcerers. These fall under those capable of great harm. They are certainly considered to have powerful spirits, but they can’t be considered to be universally harmful. In their way they typify all Mesopotamian demons. They are not good or evil by nature, but rather do what they do because of who they are as individuals.
Udug: The Udug demon is a generalized demon. Udug seems to be a generalized word for demon. Asag, Galla, and many other demons can be grouped under this term.
The term Udug Hul is often translated as evil demon, but it more properly refers to a hostile demon. All demons have a good side and a bad side even if we do not know everything about the demon. If you are on the receiving end of a demon’s bad side then that demon is an Udug Hul.
Asag: Griffin like desert demon. The Asag is a man with wings and often a birds head.
In the Sumerian poem Lugale, the Asag is a monstrous demon who is defeated by the god Ninurta/Ningirsu (God of the south wind, irrigation and coppersmiths. Also a hunter and a warrior deity.) The Asag was hideously repulsive in appearance and his power caused fish to boil alive in the rivers. He was born from the mating of An (the father of the gods) and Ki (primordial earth), and the Asag himself mated with the kur (mountains) to produce offspring. He was accompanied by an army of stone allies (the stones of the mountains).
Lilitu: Owl like wind demon known for killing infants and mothers.
Lilith is the Babylonian name simply identifying her as a specific Lilitu demon. Lilitu demons first show up in the Gilgamesh myths. In the Sumerian version of these myths no specific demoness is mentioned, but in the later Babylonian versions she is always called Lilith.
She is a Lilitu demon, but what is a Lilitu demon? Lilitu demons tell us a lot simply in their name. “Lil” means wind, “itu” means moon. Moon wind together, however, means owl. The Mesopotamian screech owl is a creature that glides silently on the wind with a moon like, disturbingly human, face. They are disturbingly large and carry off the young of various creatures.
In Gilgamesh, the Liltu demoness was living in a tree and acting much like a harpy. This type of wind spirit is a female who preys upon the lives of babies and expecting mothers. Gilgamesh frightened it away with his enchanted Ax of the Road after killing a snake monster.
Lilitu were one group of a triumvirate of demons. Lilitu and Ardat Lili, meaning maiden lilu, are female groups of demons, and Lilu are male. Each of them preys upon a select type of victim. The shared lil prefix in each of their names tells that they are each wind demons.