The edimmu, read incorrectly sometimes as ekimmu, were a type of utukku in Sumerian religion, similar in nature to the preta of the Hindu religions or the jiangshi of Chinese mythology. They were envisioned as the ghosts of those who were not buried properly. They were considered vengeful toward the living and might possess people if they did not respect certain taboos, such as the prohibition against eating ox meat. They were thought to cause disease and inspire criminal behavior in the living, but could sometimes be appeased by funeral repasts or libations. The edimmu were also thought to be completely or nearly incorporeal, “wind” spirits that sucked the life out of the susceptible and the sleeping (most commonly the young).

There you go. Origin of Mesopotamian undead, right there. Not that Labyrinth Lord or Swords & Wizardry have stats for Ghosts. They do have stats for Shadows, though. Although Labyrinth Lord explicitly states Shadows are not undead, Swords & Wizardry embraces the ambiguity. Since I’m using Swords & Wizardry stats for monsters, that’s just as well.

Shadow

• Hit Dice: 2+2
• Armor Class: [12]
• Attacks: 1 touch (1d4 + STR drain)
• Saving Throw: 14
• Special: Drains 1 STR with hit, can only be hit by magical weapons
• Move: 12
• Alignment: Chaos
• Challenge Level/XP: 4/120

Shadows may or may not be undead creatures: they are immune to Sleep and Charm, but the Referee may decide whether they are undead creatures subject to turning or whether they are some horrible “other” thing: a manifestation, perhaps, or a creature from another dimension (or gaps in the dimensions).
Shadows are dark and resemble actual shadows, though they may be even darker in coloration. They are not corporeal, and can only be harmed with magical weapons or by spells. Their chill touch drains one point of Strength with a successful hit, and if a victim is brought to a Strength attribute of 0, he or she is transformed into a new shadow. If the person does not come to such a dark ending, then Strength points return after 90 minutes (9 turns).

Labyrinth Lord